Fixes https://github.com/flutter/flutter/issues/18200.

This should fix https://github.com/flutter/flutter/issues/18729

I'll add a gold test, and try to figure out how to remove the saveLayer without affecting the correctness later.

This should fix https://github.com/flutter/flutter/issues/18731 and I've added a unit test for it.

Introduced in d248725e, but has been red
since landing. Marking flaky rather than reverting since it's the only
failure.

The `flutter attach` test was failing because the Android device had
the app already installed.

Add `flutter attach` command.

This command allows Flutter to connect to applications that haven't been launched using `flutter run`.

Unbreaks flutter-build

* Revert changes to core SDK members that haven't been propagated to the g3 Dart SDK yet.

* Respond to comments.

* Remove retype

* Temporarily un-remove VMService.retype to unblock g3 roll

* Checkout back to master, we need fewer changes to reach compat with dev.61 than dev.60

This prevents the error:

`type 'List<dynamic>' is not a subtype of type 'List<Map<String, dynamic>>' `

The test added fails when dart_vm.dart is reverted to `master`, and succeeds in
its current state.  This issue was run into while connecting to the
Dart VM.

This fixes https://github.com/flutter/flutter/issues/18708

* Suppress stdout compile diagnostic when compile expressions.

This fixes https://github.com/flutter/flutter/issues/18574.

* Use equal sign for default values

* Revert "manual rollback of of 18530 (#18531)"

This reverts commit 3f79f8cb.

* Fix the offset calculation

* Add a unit test

* Bump mockito to 3.0.0-beta

* Few fixes

* fix test

* Bump image

* Fix

* New packages update

* With matcher pinned

* No more typed

Move the notch computation from the FAB to the BAB.

The notch in the BAB (bottom action bar) for the FAB (floating action button) was previously kept as part of the FAB's implementation. This was done to keep the shape of the FAB and the shape of the notch coupled.
That approach resulted in a somewhat complex and 'non Fluttery' mechanism for propagating the notch computation from the FAB to the BAB.

This CL uncouples the FAB and the notch computation.
With the new API the BAB computes its overall shape including the notch using a NotchedShape delegate.

This includes multiple breaking changes:
  * Scaffold.setFloatingActionButtonNotchFor is deleted.
  * The ComputeNotch type is deleted.
  * The hasNotch property of BottomAppBar is deleted.
  * The notchMargin property of FloatingActionButton is deleted.

Quick migration guide from the previous API:

| Previous API | New API |
| ------------------|-------------|
| BottomAppBar(hasNotch: false) | BottomAppBar() |
| Using a FloatingActionButton with: BottomAppBar() / BottomAppBar(hasNotch: true) | BottomAppBar(shape: CircularNotchedRectangle()) |
| Scaffold.setFloatingActionButtonNotchFor(..) | No longer supported |

This is a follow up on https://github.com/flutter/engine/pull/5420
and https://github.com/flutter/flutter/issues/18057

As you can see from the diff, we also mistakenly saveLayer before
the clip at some places previously.

* Use RenderAnimatedOpacity within AnimatedOpacity widget (#15466)

* Fixed minor bug in RenderAnimatedOpacity

* Updated protected API for ImplicitlyAnimatedWidget

* Serialize compilation requests.

* update tests for TextStyle changes in engine

* roll engine, support Foreground on TextStyle

* roll to TextStyle.foreground

* add tests, update docs, fixes from tests

* add golden tests

* stroke + gradient

* update goldens hash

* Use centered widget

* fix typo

* Disable golden tests until Linux generated files are available

* update goldens