* Simplified the serialization/deserialization logic of the Descendant/Ancestor matchers

* Added a composable waitForCondition Driver/extension API.

This reverts commit df2db4e5.

* Added SerializableWaitCondition for communicating between driver script on host and extension on device.

This reverts commit 8edc3f76.

This relands https://github.com/flutter/flutter/pull/35297

The followings have been done to fix the broken tests:
  1. Add `didSendFirstFrameRasterizedEvent` extension and its tests
  2. Wait for `didSendFirstFrameRasterizedEvent` instead of
     `didSendFirstFrameEvent` during start up tests
  3. Mark missed (probably newly added) start up tests as flaky

This reverts commit 68fc7231.

This should fix https://github.com/flutter/flutter/issues/31442 and https://github.com/flutter/flutter/issues/34867

* Add semantic label finders

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

* Emulate text entry in FlutterDriver

* document enterText behavior

* remove the unnecessary composint TextRange

This patch reorganises flutter_driver's lib/src directory into three
subdirectories:

* driver: sources transitively imported/exported by flutter_driver.dart,
  which defines the API used by driver tests executed on the host machine.

* extension: sources transitively imported/exported by
  driver_extension.dart, which defines the API used to instrument a
  Flutter app running on the target device for use with a driver test.

* common: sources common to both driver and extension code.

This makes rolling Flutter into repositories that use Bazel (or
Bazel-like build systems) significantly more robust, due to the simpler
glob patterns involved.

Mainly, this adds documentation to members that were previously
lacking documentation.

It also adds a big block of documentation about improving performance
of widgets.

This also removes some references to package:collection and adds
global setEquals and listEquals methods in foundation that we can use.
(setEquals in particular should be much faster than the
package:collection equivalent, though both should be faster as they
avoid allocating new objects.) All remaining references now qualify
the import so we know what our remaining dependencies are.

Also lots of code reordering in Flutter driver to make the code
consistent and apply the style guide more thoroughly.

* comprehensive list of lints
* add comments to commented out lint
* fix unnecessary_this lints
* exclude prefer_final_fields

As per the recent fix to the `always_specify_types` lint (https://github.com/dart-lang/linter/issues/199), literal maps and lists are now expected to be explicitly typed.

Running that lint on the repo identifies quite a few spots to update.  This focuses on `flutter_driver` and `flutter_sprites` (somewhat arbitrarily) but the changes are fairly representative.

Note there are a number of places where I made a quick judgement on how specific to make the types.  Feedback on those is welcome.  (Especially as we move forward with more.)

* [driver] "waitFor" command in place of broken "exits"

* [driver] wait using frame callback