fuchsia_tester.dart still assumes Dart 1. Previously, it ran tests directly
from source, flutter_platform.dart automatically runs a kernel compile when
operating in Dart 2 mode, but this assumes a functional Dart SDK is available
in the artifacts directly, and fuchsia_tester.dart mocks out the artifacts
directory with an empty temp dir.

Remaining work is:
1. Get the frontend server building as a dependency on Fuchsia.
2. Patch fuchsia_tester.dart to use a valid Dart SDK and frontend server.

This also reverts migration to Dart 2 typedef syntax.

This reverts commit 6c56bb24. (#18362)
This reverts commit 3daebd05. (#18316)

Now that Dart 1 is turned off, reapplying my change to turn on the prefer_generic_function_type_aliases analysis option, and fix all the typedefs to Dart 2 preferred syntax.

Also eliminated the unused analysis_options_repo.yaml file and turned on public_member_api_docs in analysys_options.yaml.

No logic changes, just changing the typedef syntax for all typedefs, and updating analysis options.

Revert "Update typedef syntax to use Function notation and turn on lint for old notation. (#18035)" (#18041)

This reverts commit 32586020.

Fixes #18028

Just changes typedef declarations, no logic changes.

Fixes https://github.com/flutter/flutter/issues/14492

* scrolling node eleminated

* remove second node

* fix ids

* Do not crash when toggeling Semantics on, off, on

* review comments

`RenderSemanticsGestureHandler` is no longer a semantics boundary, which allows us to correctly mark disabled buttons as disabled without having their semantics size and semantics node id change unexpectedly.

Fixes https://github.com/flutter/flutter/issues/12589.
Fixes https://github.com/flutter/flutter/issues/11991.
See also https://github.com/flutter/flutter/issues/11993.

This change also required some refactoring to how we deal with `twoPaneSemantics` scrolling as it previously relied on `RenderSemanticsGestureHandler` being a semantics boundary. This should also make the underlying logic easier to understand.

In addition, the following minor changes are included in this PR:
* Removal of orphaned and unused `SemanticsConfiguration.isMergingDescendantsIntoOneNode`.
* Logic optimizations for `markNeedsSemanticsUpdate` .
* Fix for edge case where `MergeSemantics` failed to merge semantics.
* Use of emojis to better indicate leaf merging in the printed semantics tree.
* Better assert message for adding invisible child semantics nodes.
* Make some semantics tests robuster by not relying on creation order of SemanticsNode ids across test boundaries.

Fixes https://github.com/flutter/flutter/issues/13943.

* Send scroll progress with ScrollCompletedSemanticsEvent

This requires engine change https://github.com/flutter/engine/pull/4144

* fix analyze warning

* review comment

* Roll engine to 45b11f742d38ebf564a5a832b1af00661d1a31fa

* fix test

* Show accessibility frame while scrolling

* ++

* fix test

* ++

* ++

* ++

* ++

* ++

* dart docs

* test fix

* undo unintended change

* fix test

* fix test

* review feedback

Add Diagnosticable base class and documentation

Refactor RenderObject.toStringDeep and Widget.toStringDeep code to use DiagnosticsNode.

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.

* Expose the currently available semantic scroll actions

* review comments

* add test

* refactor to set

Fixes https://github.com/flutter/flutter/issues/8476

More detailed list of changes in this patch:

* Replaced the didTouch special logic with more generic logic that
  uses Activities instead. Now instead when you tap down the
  Scrollable calls `hold()` which begins a HoldScrollActivity which is
  a hybrid of DragStartDetails and IdleScrollActivity and can be
  canceled. When you let go, it gets canceled and that goes ballistic.

* Make DragGestureRecognizer more aggressive about grabbing pointers,
  otherwise a second pointer in a situation with competing horizontal
  and vertical recognizers always gets taken by the other one.

* Fixed the _GestureSemantics widget to call the "down" callbacks so
  that it follows the same pattern as "real" interactions.

* Added tests for the above.

* Added a hashCode to ScrollActivity.toString (and subclasses).

* Added a toString to ScrollDragController, and include it in
  DragScrollActivity's toString.

* s/coorindator/coordinator/

* Add a comment in DragStartDetails to distinguish it from the
  otherwise identical DragDownDetails, so we're not tempted to merge
  them.

This patch reworks some of the guts of scrolling to make it easier to
implement nested scrolling effects. The actually nested scrolling effect
will be included in a later patch.

* more widget const constructors

* prefer const constructors

* address review comments

Rename State.config to State.widget
Rename State.didUpdateConfig to State.didUpdateWidget
Renamed all State subclasses' local variables named config to something else

The new name matches the style guide. (The old name was just old and predated
the style guide.)

Fixes #8000

Covers lib/ in package:flutter.

Rename all the "2" classes related to scrolling to remove the "2". Now that the
old scrolling code is gone, we don't need to use the suffix.

All the clients have migrated to Scrollable2.

The replacements are ListView and SingleChildScrollView, respectively.