Updated row and spacer handling for Escalator.

Main changes:
- Spacers are only maintained and checked for rows that have DOM
representation, and not at all if there is no details generator. This
gives notable performance improvements to some particularly large Grids
- Escalator no longer tries to trim away any rows that don't fit within
the viewport just because a details row gets opened in Grid. This leads
to some increase in simultaneous DOM elements, but simplifies the logic
considerably. For example opening or closing details rows doesn't
require checking the overall content validity beyond the details row
itself anymore, but some repositioning at most. There are also no longer
any orphaned spacers without corresponding DOM rows.
- Spacers are better integrated into the overall position calculations.
- Some public methods that are no longer used by Escalator or have
changed functionality or order of operations. Any extending classes that
tap into row, spacer, or scroll position handling are likely to need
reworking after this update.
- Auto-detecting row height is delayed until Escalator is both attached
and displayed.

* Add explicit handling of ctrl-a

Fixes https://github.com/vaadin/framework/issues/11678

* Adds test case and formatting the code

* Ensure the upload button has been disabled when calling from succeedListener with Push enabled

* Add Tests to verify

Fixes #10741

- Escalator should notify when an existing details row is moved to a new
index.
- Grid and DetailsManagerConnector should update their internal indexing
when details manager index changes in Escalator.

* Fixes #11642. ComboBox with pageLength 0 should be updated if DataProvider changes

* added comments, fixed imports

- Initial fix attempt interfered with selection events, added regression
testing for those and found a better way to ensure shift selection works
on IE11 also with Windows 7.

Fixes #11608

* Fix unstable tests

* Add Delay to unstable tests

* Add sleep time

* Adding "v-grid-editor-selected" stylename in editor cell wrapper element when Grid is opened on selected row.

* Clicking on DateField pop-up should select Month/Year

In Year/Month Resolution DateField should select the value, when user clicks on pop-up

Fixes #8447

* add test case

* Limit the workaround for non-push mode

Fixes #11616

Fixes #11608

* Using @Delayed annotation for DateField Rpc

* Separate a rpc for handling the time change in DateTimeField

* Add test case for wrong event order

* #11614: Added test which demonstrates that the fix is incomplete

* #11614: UI.doRefresh() only calls navigator when the navigation state actually changes

* Added javadoc to Navigator.getCurrentNavigationState()

* Minor: Removed accidental star imports

1) recalculate the offset, as ChromeDriver starts to follow the standard;
2) update screenshots;
3) correct the `click()` call with using coordinates, related to 1)
4) `sendkey()` with using key.modifier adjustment
5) add sleep 
6) workaround for mastery failures

* Fix regression that broke PreserveOnRefresh functionality with Navigator

Fixes https://github.com/vaadin/framework/issues/11614

Old patch https://github.com/vaadin/framework/issues/11416 calls navigateTo allways when Navigator is present, which is wrong, since it is needed only when navigation state has truly changed.

* Add test to the fix

* Recalculate the column widths before the first row is added

Fixes #11607

* Grid Editor: make Tab key skip read-only/disabled fields

Closes #11584

* Extracted DefaultEditorEventHandler.getDeltaFromKeyDownEvent() which allows for easy further Grid Editor customization

* Make DefaultEditorEventHandler.Delta public so that getDeltaFromKeyDownEvent() can be overridden

* Fixed exception in isEditable() if the widget was not a Field

* Refactored DefaultEditorEventHandler.Delta to CursorMoveDelta which expresses the intent more clearly

* Merge branch 'master' into master

* Fix grid column reordering

Fix grid column reordering when there are hidden columns and footerRow.join

* Add test

* Fix duplicate grid column visibility change event

Toggle a column visibility through UI will fire 2 event. There should be only 1.

* Add Test

* Grid editor: TAB now skips non-editable columns

Pressing TAB would shift the focus to non-editable cells when the Grid was in edit mode.
This patch makes DefaultEditorEventHandler to skip such columns.

Closes #10970

* Add tests

- limit DataCommunicator workaround from #11320 to ComboBox only
- don't reset DataCommunicator before modifying all sorting data

Fixes #11532

* Code format

* Merge branch 'master' into code-format

- Replace the GridDisabledTest screenshot usage
- Replace the screenshot tests in BasicCrudGridEditorRowTest
- Replace the screenshot tests in ComboboxVaadinIcons
- Replace the screenshot tests in ValoThemeUITest::accordions
- Added screenshotcomparetolerance to some screenshot test to make tests stable

issue in #11343 and #11385 is not reproducible on top this patch
Three different bugs are involved in this fix:
we bring the old fix(#11094) back and fixed the other related issues:
1) allow adding the same new item after dataProvider got reset, This is cause by the client side parameter `LastNewItemString`, it saves the value added before resetting. 
2) clear the pending newItem eagerly, so that the same value will not be added again.

* Clicking on slider makes handler move

Fixes #1496

* Introducing control over clicking behaviour

- User will have to enable process of the click event on handle calling `slider.setEnableClickHandler(true);`
- Clean-up the handler logic in VSlider.java
- Renaming the property to `updateValueOnClick`
- Added JavaDocs
- Fixing tests

* Add delay to the unstable test

* Fixes 11517. Use ENTER and SPACE keys as shortcuts for header buttons

* Merge branch 'master' into fix-11517

* Increase sleep time for test failing in validation

* Merge branch 'master' into fix-11517

* Reset selection on DataProvider change in RadioButtonGroup

Fixes #11454

Other components needing the same fix are ListSelect,NativeSelect,Combobox (The ones implementing HasDataProvider and extending AbstractSingleSelect. Grid is not affected as it extends AbstractListing and hadles selection differently)

* Added test case

Verify that ValueChangeListener is actually fired after value is reset setting new DataProvider

Fixes 11528

Verify that correct mode(HTML/TEXT) of caption is set for the  Panel
Fixes #11521

Add DataChangeHandler removal in v7 Grid just as in v8 Grid.
Adding tests to the fix to verify, that NPE is not thrown.

Add check for the V8 TextField used in Table in compatibility mode. This makes clicking cell with the TextField select the row, preserving behaviour from V7.
Through, as it's noted also before, this is an improved workaround, not a proper solution to address the issue.

Fixes #11474

Explicitly reset the value in case if it was cleared.
Ignore the case for selecting a suggestion.

Fixes vaadin/testbench#1122

* Add Test file

* Remove redundant check for for Firefox

It seems that in older versions of Firefox (at least, older than 45) the KeyPress event should be used instead of KeyDownHandler. At some point (works already on 58 version, the current one is 65) the issue was resolved and starting from Firefox 65 this hook prevents from navigating in the pop-up via keyboard.
Simply removing additional logic makes navigating in both DateField and InlineDateField possible

Fixes #11465

* Fix an NPE caused by the previous fix to Grid's frozen columns (#10653)

If the user managed to get two frozen column count changes into a single server round-trip before the component had been attached, the previous fix  #11346 lead to a null pointer exception since there was no diff state available.

This fix adds a null check before removing the frozen column count value from the diff state so that this will not happen.

Closes #10653

Clear contents of iframe clone that is in a Window so that when it's reattached to DOM we don't get 404

* add possibility to configure nested null behavior to Grid.Column

* added addColumn method that allows configuring the nested null handling behavior of the column

* added uitest for nested null value handling, implements #11137

* Some formatting changes

* add client side integration for custom styles for checkbox.label and checkbox.input

* add server side integration for checkbox element styling

* add server side tests

* add client side test

* Improve VMenuBar click handling logic

During `updateFromUIDL` inside MenuBarConnector we empty and re-instantiate the components of MenuBar. When we are modifying the Menubar from the BlurEventListener of another component, we ,by this, remove widgets, therefore clickEvent is not fired and the action of the MenuItem is not proceed as a result. (The BlurEvent is fired before the click event in the chain of events. )

To improve the situation, we catch onMouseDown event , which is fired before BlurEvent,by assigning mouseDown flag to true. Then if no click event has yet happened, we delay the execution of update inside `updateFromUIDL` by default 500 ms. Then if click event occurs, it proceeds normally. The time can be increased/decreased using setter.

There is no delay, if we are clicking on the MenuBar as usual or no Blur listener is set.

This change allows setting descriptions

* Remove accidentally committed comment

* Don't update the state on the getDelayMs call

* Fixes #10814

* Add missing tests

Fixes #11374

* Move onClick logic to the Connector

Move onClick event handling from 'VNativeButton' to NativeButtonConnector. Now works as for regular button.

Also, adding propagation of the `enabled` value to the state on disableOnClick being true

Fixes https://github.com/vaadin/framework/issues/11188

Setting read-only state to CheckBoxGroup should disable adding clicking effect. Missing v-readonly style is added to every CheckBox in the component, if it's set to read-only.

Fixes: https://github.com/vaadin/framework/issues/11113

* Add file missed from initial commit

* Verifying that option is enabled

Some of the options might be disabled on there own. Verify that option is not disabled, before removing disabled styles.

* Add missing test file