* Reland "Updated background execution implementation for Android" w/ JNI fixes for merge breakages

This reverts commit 5442c0a7.

This reverts commit bc885f31.

These are making some of the tests that are sensitive to output flakey.

This allows applications to start a Flutter engine instance during app startup
and keep it running throughout the app process' lifetime.

FlutterActivity subclasses can override createFlutterNativeView to provide a
preinitialized FlutterNativeView instance and override retainFlutterNativeView
to signal that the FlutterNativeView should be kept alive when the activity
is destroyed.

* do not pause rendering when android view loses focus

This reverts commit c83d1ef1.

* do not pause rendering when android view loses focus

https://github.com/flutter/flutter/issues/14519

* Turn on strong mode by default when a platform file is present in the
bundle instead of using a flag passed into the engine which might not be
true when we invoke an installed app.

* - Roll dart to version fe96de2858f078e4ad04f8f30640184bf3d8102d

* Update license file.

Add support for --strong option in the engine, create a strong mode version of the platform file (#4504)

* Add a --strong option to the front end server so we can use strong mode with preview-dart-2.

* Plumb the --strong option through the dart controller into the VM.

* - Build a strong version of platform.dill for use with the engine.
- Fix a strong mode static error in the assert statement

* Enable asserts when running debug version even in strong mode.

* Use the correct platform dill file for linking when doing the aot builds.

* Fix formatting issue.

[Android] Allow persisting a FlutterNativeView across activities.

Skia tracing is extremely useful for internal debug, but reduces the
amount of space available in the Dart Timeline buffers.
Disable skia tracing by default and expose them via the --trace-skia
flag.

Create platform API for first frame callback. Use for defer hiding splash screens on Android and iOS (#3956)

* Add back launch screen view until first frame on iOS

* improvements

* Move callback plumbing from ios surfaces to the gpu rasterizer. Didn’t wire java JNI yet.

* Android JNI

* Fix ios reference count and let android engine manage a view on top with launch screen

* Hook up Android activity and view

* review notes

* review notes

* Move thread switching upstream. Use weak references for callbacks.

* Some clean up

Sometimes, plugin instances need access to the `FlutterView`.
They can currently cast the `messenger()`, but that's fragile.
This adds API support for getting the view from the registry.

* Revert "Fix licenses_lib golden file (#3798)"

This reverts commit d8ac43c3.

* Revert "Remove ParagraphConstriants (#3796)"

This reverts commit 8ccf767f.

* Revert "Reland "Initial integration of libtxt with Flutter alongside Blink." (#3793)"

This reverts commit 3c049219.

See https://github.com/flutter/flutter/issues/10813

* Transition to Hybrid lib/txt and blink text system.

* Revert "Enable line join styles and miter limit. (#3777)"

This reverts commit 5403f65b.

* Revert "Revert "Update switches to use StringView." (#3784)"

This reverts commit 80f039ff.

* Revert "Initial integration of libtxt with Flutter alongside Blink. (#3771)"

This reverts commit c548c65b.

This factors the functionality that was in `FlutterActivity`
to live in `FlutterActivityDelegate`. This will allow the creation of a
`FlutterFragmentActivity` that has the same core functionality, which in
turn unlocks certain Android plugins that choose to require the v4
support library (like Google Sign-In).

https://github.com/flutter/flutter/issues/10072