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

Update screenshots due to update of search-minus and search-plus icons values

* 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

* Request data update before client response

* fix the accidental commit

* add tests

fixes #11320

* Add missing FocusShortcutListener

Was removed from 8.0 and not readded.

Fixes #8297

* Update Release note for this change

In certain cases setting the frozen columns didn't produce the expected result in the client side widget state. This happened if the frozen columns value was set to be the same it was before removeAllColumns was called.

This fix removes the frozen column value from the diff state so that the value gets properly set in the client side.

Closes #10653

* Add more context information to criteriaScript in GridDropTargetConnector

When using drag and drop in Grids and TreeGrids a criteriaScript can be specified.
However, this criteriaScript only gets an event as input parameter.
It would be helpful if the criteriaScript would get more information:
- the DropLocation
- the targetElement which is used as a base for the DropLocation

This change provides a protected method in DropTargetExtensionConnector
which decides, if the drop is allowed by the criteriaScript.
This method is overriden in GridDropTargetConnector to
provide the both parameters dropLocation and targetElement.

* add Test UI for criteriaScript with targetElement and dropLocation

* add some description for the Test UI

- When rows are added, details row heights need to be taken into account
in positioning.

Fixes #11348

* Fix colorPicker tests

In IE11, the click-layer needs longer time to load.

* Revert "Update ComboBox internal state on new item added (#11094)"

This reverts commit 56ce91c616.

* Add tests to verify the issue

* Fix for setting default row height for a Grid with details row(s) open.

- Details row(s) should be taken into account when the rows are
re-positioned after getting new heights.

Fixes #11325

This refactoring addresses two issues cased by dropping updatedData before it was processed. Issues arise , when visibility has change.

Fixes #11274 and similar issue within RadioButton

There is no reliable way to test automatically NativeSelects in Grid, but adding UI test, at least

Fixes #11276 

Refactor the code and correct the logic for validation

Rename an internal variable, as it contains more than one type of messages

Fix upload issue

* Make value changes in color picker user originated

This is not a programmatically initiated event, so it should have the
'userOriginated' property set to 'true'.

 - Added test to verify that indeed event is user originated after the change

* Add Test for closing window with focused textfield

verify issue #10642

* Refactor the code about using keyMapper

Fix https://github.com/vaadin/framework/issues/11268

```buildTime()``` function re-initializes ListBoxes for hours,minutes and seconds values. We need to set correct values in those ListBoxes, before assigning value to the labels displayed instead of those ListBoxes in ReadOnly state, as , otherwise, the selectedItemIndex returns 0.

* Fixes #10937

- Previously if selected value is null, then index is set to -1; in current implementation if value is null and emptySelection is allowed then set the index to 0. (The position for the empty selection)

- Also, if changing the allowEmptySelection on the fly, ensure, that either index is to-reset to -1 by setting the selected value to null on the client-side (the value before was null) or preserve the value(value was different than empty).

* Change the test case

Since in this pr the behaviour of the NS is changed, therefore old test need to be adjusted.

Change: setting null as value will select empty selection. Before that nothing would be selected and value will be cleared.

Behaviour change in PR: Allow selecting null as value

* Rebuild calendar pop-up on readOnly state change

Fixes https://github.com/vaadin/framework/issues/6565

* Test case for removing Grid with components

* This reverts commit b2745dc14f.

Add test case to address the issue with removing gird with components;
Current situation: the grid cannot be removed and client-side throw an error. 
fixes: Revert the corresponding change, as it didn't address any issue which was fixed.

- When a TabSheet is scrolled to an end and then resized bigger, more
tabs should appear to the left.
- When a TabSheet is right-aligned in Valo and scrolled to the end, last
tab shouldn't be partially hidden behind the scroller buttons.
- Shouldn't allow attempts to scroll into directions where there is
nothing left to scroll to, even if the current tab isn't fully visible.

Fixes #807

- Multiple headers shouldn't stack behind each other.
- Body rows shouldn't get stuck to default row height.
- Compatibility version's hidable row selector shouldn't try to
calculate row heights based on rows that haven't been added to DOM yet.

Fixes #7674

* Suppress unavoidable UIDetachedException

Fixes #11144

- More lightweight, and fixes things for any custom implementations of
Escalator as well.

Fixes #11044

* update uitest screenshot reference

* one more screenshot

* screenshot for table drop indicator

Fixes #11087

* discardStaleCacheEntries is moved to a proper place before updating indexToRowMap and keyToIndexMap maps. In its previous place, it cleared the data that was just put in the maps.
Fixes #11143

* Adding test

* Removing extra annotations

* Updating chrome version to 69 in tests (#11182)

* Updating Chrome version to 69

* Updating screenshots taken in Chrome 69

* Fixing screenshots

* Fixing screenshots

* Adding some wait commands to tests

* Fixing screenshots

* Revert: Fixing screenshots

* More screenshots

* - Adding wait commands to make sure the transitions end before screenshot
- Fixing a screenshot

* Correcting a mistake of using wait instead of sleep

* Fixing more screenshots

* Increasing the height of ContextMenu (Because of limitation of new Chrome 69 in terms of minimum window height, ContextMenu size can't be tested with a small height.)

* Updating Chrome version to 69

* Updating screenshots taken in Chrome 69

* Fixing screenshots

* Fixing screenshots

* Adding some wait commands to tests

* Fixing screenshots

* Revert: Fixing screenshots

* More screenshots

* - Adding wait commands to make sure the transitions end before screenshot
- Fixing a screenshot

* Correcting a mistake of using wait instead of sleep

* Fixing more screenshots

* Increasing the height of ContextMenu (Because of limitation of new Chrome 69 in terms of minimum window height, ContextMenu size can't be tested with a small height.)

Fix handler creation to happen on init

Ensure that HeaderRow is not null in Grid

Fixes #10485

Fixes #11099