Make Element tree root generic

Reland "Introduce the PipelineOwner tree (#122231)"

This reverts commit f73c358e.

Introduce the PipelineOwner tree

Fix how tests count open SemanticsHandles

* lerp documentation

* Remove Note, Note That from repo

* Improve BorderSide documentation.

* apply review comments

* Remove superfluous words.

* Update packages/flutter/lib/src/widgets/slotted_render_object_widget.dart
Co-authored-by: Michael Goderbauer <goderbauer@google.com>

Reland "Inject current FlutterView into tree and make available via `View.of(context)` (#116924)" (#117244)

* Reland "Inject current `FlutterView` into tree and make available via `View.of(context)` (#116924)"

This reverts commit 9102f2fe.

* remove window placeholder

Revert "Inject current `FlutterView` into tree and make available via `View.of(context)` (#116924)" (#117214)

This reverts commit a34e4194.

* enable View.of

* tests

* ++

* greg review

* rewording

* hide view from public

Add "excluding" optional parameter to TargetPlatformVariant to communicate cases where test should be ran everywhere but specific platforms (#106216)

added "excluding" optional parameter to targetPlatforms.all
Co-authored-by: Anthony Oleinik <oleina@google.com>

* Use `curly_braces_in_flow_control_structures` for `packages/flutter_driver`

* Use `curly_braces_in_flow_control_structures` for `packages/flutter_goldens`

* Use `curly_braces_in_flow_control_structures` for `packages/flutter_goldens_client`

* Use `curly_braces_in_flow_control_structures` for `packages/flutter_localizations`

* Use `curly_braces_in_flow_control_structures` for `packages/flutter_test`

* Use `curly_braces_in_flow_control_structures` for `packages/flutter_web_plugins`

* fix comments

* Use `curly_braces_in_flow_control_structures` for `packages/integration_test`

* fix indentation

This reverts commit cb378edc.

* Revert "Revert "Reland 2: Make LiveTestWidgetsFlutterBinding work with setSurfaceSize and live tests (#86912)" (#87233)"

This reverts commit 5b80d32a.

* Record tap positions

Revert "Reland 2: Make LiveTestWidgetsFlutterBinding work with setSurfaceSize and live tests (#86912)" (#87233)

This reverts commit b50991d6.

This reverts commit 5f792ba1.

Revert "Reland: Make LiveTestWidgetsFlutterBinding work with setSurfaceSize and live tests (#86739)" (#86823)

This reverts commit cf3d9409.

This PR fixes several bugs related to live tests, adds more tests, and completes the documentation of several methods related to pointer events. 

Revert "Make LiveTestWidgetsFlutterBinding work with setSurfaceSize and live tests (#86449)" (#86730)

This reverts commit cd78190b.