Immediately clean connectors which the client side does not know about

Fixes #9303

* Add ability to set multiple drag data generators for any drag data type
and change default to be accepted by spreadsheet applications such as Excel

Fixes #9323

* Refactor common methods of InMemoryHierarchicalDataProvider and ListDataProvider to a single interface
* Rename HierarchyData and InMemoryHierarchicalDataProvider, introduce HasHierarchicalDataProvider
* Additionally adds a helper method for recursive constructing
TreeData with a child item provider.

* Add ItemClick event to Tree
* Add collapse provider and style generator to Tree

* Refactor Html5 DnD client side based on API review

- Moved classes to "correct" packages.
- Removed method DragSourceExtension.clearDataTransferText()
- Remove ButtonDragSource in favor of more generic API

* Create upload URLs only when stream variable is attached by drop handler

* Add file size limit to test ui and remove label drop target

* Poll server for changes at the end of each file upload

First step of mobile DND support.

- Add mobile html5 dnd support using polyfill
- Adds a switch for enabling mobile html5 dnd support
- Adds polyfill only when needed
- Ignore native Android Chrome drag start because doesn't work properly
(no dragend event fired)
- Add documentation on enabling mobile HTML5 DnD support
- Add mention of drag-drop-polyfill license
- Fixed issue in polyfill when not using "snapback"
- Add mention of forked polyfill

Fixes #9174

Fixes #8891

Add (FieldEvents.FocusNotifier & FieldEvents.BlurNotifier) in AbstractTextField.
The fields TextField, TextArea and PasswordField are the only focusable input fields where this Implementation is missing.

- Always set some drag data
- Set the dropEffect on dragEnter and dragOver events on drop target
- Send the dropEffect to server on drop event with disclaimer of current support
- Remove _dragOverCriteria_ and use _dropCriteria_ for `dragenter`, `dragover` and `drop` criteria

Tested manually basic DnD and Grid DnD on Mac with Chrome, Firefox, Safari.
Safari is still missing drag image (regression).

Tested manually basic DnD and Grid Dnd on Windows IE11 and Edge.
Drop event for both is still not working properly #9174.

This patch introduces a Tree component, implemented as a Composite
using TreeGrid. As initial version of the component, some functionality
of the old Tree component has been left out for now.

Partly addresses #8617

Fixes a race condition when expanding multiple items.
Only one expand or collapse request should be sent from
the client before waiting for a response, otherwise the
indexing in subsequent requests will be incorrect.

Adds API to collapse and expand multiple items from the
server, reducing the amount of round trips with multiple
item expands and collapses.

HierarchyMapper now correctly keeps expanded nodes expanded
if their parent is collapsed.

* Add support for pluggable filters for rewriting dependencies

Fixes #9151

Addresses #8775 for version 8.1+

Fixes #6043

The parent Design must leave child handling to the nested design, when
there are no children defined in the parent Design. This fixes a problem
with com.vaadin.ui.GridLayout$OutOfBoundsException when the reading
operation of the parent design tries to set number of rows according to
its empty content.

A composite is included in the server side hierarchy and in the connector
hierarchy on the client side but does not have its own widget or DOM.

To ensure that captions etc are renderer correctly for the root contents,
the client side connector returns both the widget and state for the content
connector.

Server side API related to width and height are automatically forwarded to
the root component to enable easy use of the composite inside different
layout configurations.

Other server side API inherited from AbstractComponent is unwanted, should be
optional and therefore throw an exception by default.

Resolves #2458

Resolves #8932

Fixes #8401

Fixes #8931

Fixes #8400

Fixes #8397

It is possible to customize the drag data for each row. (#8706)

Fixes #8396

Component.setCaption has thorough Javadocs that are shadowed by a very
brief snippet in AbstractComponent and an erroneous description in
Panel. By removing those snippets, component classes will instead
inherit a much more useful description of the method.

Fixes #9050

* Add server-side expand and collapse to TreeGrid

* Add javadocs

* Fix variable naming in TreeGridHugeTreeTest

* Fix review comments

* Merge remote-tracking branch 'github/master' into 8759-server-expand

* Clear pending expands when all data is dropped

* Add documentation

Fixes #8758

Fixes #9009

* Make getValueProvider return ValueProvider

The instance can only be a ValueProvider, but the getter previously
returned a less specific type. Making the getter return ValueProvider
makes it easier to reuse the provider in other contexts that require
ValueProvider, e.g. when adding filters to a ListDataProvider.

Closes #8377

Fixes #8667

Fixes #8957

* Fix data not being sent again when adding DataGenerators

* Fix header component detaching, revert early header cleanup

Add an additional stylename `critical-error` that styles the
notification like the Error-type, but without the close button.

Fixes #8296

Fixes #8590