Revert "Notify framework to clear input connection when app is backgrounded (#35054) (#9498)" (#11720)

This reverts commit 4003fbc3.

* Implement SystemGesture.setSystemGestureExclusionRects platform channel

* Add PlatformChannelTest.java

* Fix typo in android/test/README.md

Previously the test wasn't correctly re-building the engine when its
files changed on multiple runs of `testing/run_tests.py`. It looks like
this is because the test build target wasn't depending on the entire
engine Android dependency, so some code changes were being ignored.
Update the build.

Android Embedding PR37: Separated FlutterActivity and FlutterFragment via FlutterActivityAndFragmentDelegate (#9895)

`gclient sync` now grabs Robolectric, JUnit, and their transitive
runtime dependencies. They're being stored in a new CIPD package,
`flutter/android/robolectric_bundle`.

`shell/platform/android/BUILD.gn` has a new target for building the
tests, `robolectric_tests`. `testing/run_tests.py` has been extended to
build and run the new target. Runs the android tests under
"build_and_test_android" on CI.

This also adds some very simple sample tests to start with and a README
to the java tests directory.

BSDiff is no longer used as of flutter/engine#8663. This removes the
unused Java import and sources.

New Plugin API PR3: Introduces Service, BroadcastReceiver, and ContentProvider awareness, control surfaces, and plugin bindings. (#8962)

New Plugin API PR2: Introduces ActivityAware, ActivityControlSurface, and ActivityPluginBinding. (#8943)

New Plugin API PR1: Introduces PluginRegistry and FlutterPlugin, adds support for plugin registration to FlutterEngine. (#8826)

* remove legacy build deps

Cleanup repeated rules.

Delegate a11y events and action to/from embedded Android platfrom views.

This handles delegation of:
  * AccessibilityNodeProvider#performAction
  * ViewGroup#requestSendAccessibilityEvent
  * View#onHoverEvent

Additionally updates the currently input accessibility focused node state that is
tracked by the a11y bridge when an embedded view's node is focused.

This PR mirrors virtual a11y tree of embedded platform views in the Flutter
a11y tree.

Non virtual hierarchies are not currently supported.

Only works on Android versions earlier than Android P as it relies on
reflection access to hidden system APIs which cannot be done starting
Android P.

A11y is not yet working as we also need to delegate a11y events from the
platform view to the FlutterView. This will be done in a following PR to
keep the change size a little saner.

This is in preparation for implementing platform views a11y on Android.

And e2e working prototype is available here: https://github.com/amirh/engine/tree/a11y_hacks

flutter/flutter#19418

Android Embedding PR 9: Introduce an AndroidTouchProcessor to convert MotionEvents to Flutter touch data. (#7947)

Link dart:* sources into engine for debugger source support

Currently, dart:* libraries appear to have no source in
debuggers like Observatory. With this change, these sources will be
available in debug mode applications. Sources for dart:* libraries are
lazily loaded on a script-by-script basis.

Refer to https://dart-review.googlesource.com/c/sdk/+/93375 for the Dart
SDK change.

Android Embedding PR 6: Introduce FlutterView structure with FlutterSurfaceView and FlutterTextureView. (#7896)

Merging back in after reversion. Fixed some messaging issues in FlutterNativeView and corrected some message parsing.