* Add punctuation for unterminated sentences in doc comments

* Addressing review nit

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

* Added property for expanded padding of expansion panel for solving #24071

* #24071: Renamed default const name for being more descriptive

* #24071: Improved comment of property expandedPadding

* #24071: Improved test by expanding the expansion panel by header tap + precise assertion

* #24071: Renamed property to be more descriptive

* #24071: Adjusted property comment and added missing trailing commas

* #24071: Improved test by checking real exact header size

* #24071: Added test for default header padding

* #24071: Improved comment of expandedHeaderPadding + code style adjustments

* #24071: Added missing trailing comma

* add key to constructors of public widgets

* fix a test

* fix a test

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

This attempts to reland #40186 and #41220, that were reverted in #41945.

The main modifications from the original PRs are that I predefine the shortcuts and actions maps instead of defining them inline in the build function, and I use a new mapEquals to do a deep comparison so that we don't rebuild modified things if the contents of the map haven't changed.

I also eliminated an operator== and hashCode that were defined on the Actions widget, since widgets shouldn't have those. (it's too bad though: I get an 85% speedup if we leave this in! Too bad it prevents rebuilding of the children...)

Fixes #40101

This adds a Semantics node to the Focus and FocusScope widgets, setting the focused and focusable attributes so that the accessibility subsystem can be told when a control has the input focus.

Includes an engine roll to flutter/engine@77252d2, and the following 8 engine changes:

flutter/engine@77252d2 Greg Spencer Add missing focusable testing info (flutter/engine#13013)
flutter/engine@0e42a29 skia-flutter-.. Roll src/third_party/skia 54548626a977..e27a503a0a21 (1 commits) (flutter/engine#13024)
flutter/engine@6b56ed7 gaaclarke Refactor: FlutterDartProject (flutter/engine#13006)
flutter/engine@393480c skia-flutter-.. Roll src/third_party/skia 77dde599c98a..54548626a977 (1 commits) (flutter/engine#13023)
flutter/engine@080b89d skia-flutter-.. Roll src/third_party/skia 2b1a25a4d324..77dde599c98a (1 commits) (flutter/engine#13021)
flutter/engine@90b0f30 Ben Konyi Roll src/third_party/dart f4a72bfc64..bb04f145b2 (18 commits) (flutter/engine#13020)
flutter/engine@049fb89 skia-flutter-.. Roll fuchsia/sdk/core/linux-amd64 from q_uYX... to cknsi... (flutter/engine#13019)
flutter/engine@6925b2a skia-flutter-.. Roll fuchsia/sdk/core/mac-amd64 from wuAtw... to u0JpE... (flutter/engine#13018)

Related Issues
Addresses #40101

Landing on red in order to fix the build: it's red because of the needed engine roll.

- Move `setState` to only be invoked when guarded by `widget._allowMultiplePanelsOpen`, fixing the case for `ExpansionPanelList`

- Remove setting `_currentOpenPanel` to `widget.initialOpenPanelValue` in `didUpdateWidget`, since this should only occur on `initState` and not every time the widget is updated. This fixes the problem for `ExpansionPanelList.radio`

- Added a `didUpdateWidget` condition for when `ExpansionPanelList` changes into `ExpansionPanelList.radio` to open the panel at `widget.initialOpenPanelValue`

- Added test cases for regression, expansionCallback cases, and `didUpdateWidget` transitions between `ExpansionPanelList` and `ExpansionPanelList.radio`

* Re-enable const

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

It was causing problems rolling Flutter into Fuchsia

* Just commiting two files now

* Fixed one tab

* Fixed latest changes

* Changed the data structure from a map to a single radio panel object

* A few more changes

* Fixed change from expansion radio to regular list

* Fixed change from expansion radio to regular list2

* Changed the radio constructor

* Last fixes

* Final commit

* Actual final commit

* Last change

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

Previously, ExpansionPanel would do weird things if interacted with
when it was already animating. This is fixed and there's now a test.

Also:

 * Minor fixes to make the gallery work in RTL, not that there's
   any way to see that without hard-coding the framework to RTL.
   But at least I'll be less annoyed when doing that.

 * Some trivial code and documentation cleanup.

* _SaltedKey solution to `ExpansionPanelList`

_SaltedKey implementation courtesy of @Hixie
Tested and confirmed working.
Fixes #11166

* Added a simple test

* Style correction to test

* Introduce a Directionality inherited widget which sets the ambient LTR vs RTL mode (defaulting to null, which means you cannot use directionality-influenced values).

* Make it possible to configure Padding (including Container.padding and Container.margin) using a directionality-agnostic EdgeInsets variant.

* Provide textDirection and verticalDirection controls on Row and Column to make them RTL-aware.

* Introduce a variant of FractionalOffset based on the EdgeInsets variant. Not yet actually used.

* Fix all the tests that depended on Row defaulting to LTR.

This widget is a replacement for ScrollableViewport that uses the new
Scrollable2 machinery. The widget is not based on Slivers but does use the new
scroll behavior classes.

Renamed expansion_panels.dart to expansion_panel.dart.

Previously, pumpWidget() would do a partial pump (it didn't trigger
Ticker callbacks or post-frame callbacks), and pump() would do a full
pump. This patch brings them closer together. It also makes runApp run a
full actual frame, rather than skipping the transient callback part of
the frame logic. Having "half-frames" in the system was confusing and
could lead to bugs where code expecting to run before the next layout
pass didn't because a "half-frame" ran first.

Also, make Tickers start ticking in the frame that they were started in,
if they were started during a frame. This means we no longer spin a
frame for t=0, we jump straight to the first actual frame.

Other changes in this patch:

* rename WidgetsBinding._runApp to WidgetsBinding.attachRootWidget, so
  that tests can use it to more accurately mock out runApp.

* allow loadStructuredData to return synchronously.

* make handleBeginFrame handle not being given a time stamp.

* make DataPipeImageProvider.loadAsync protected (rather than private),
  and document it. There wasn't really a reason for it to be private.

* fix ImageConfiguration.toString.

* introduce debugPrintBuildScope and debugPrintScheduleBuildForStacks,
  which can help debug problems with widgets getting marked as dirty but
  not cleaned.

* make debugPrintRebuildDirtyWidgets say "Building" the first time and
  "Rebuilding" the second, to make it clearer when a widget is first
  created. This makes debugging widget lifecycle issues much easier.

* make debugDumpApp more resilient.

* debugPrintStack now takes a label that is printed before the stack.

* improve the banner shown for debugPrintBeginFrameBanner.

* various and sundry documentation fixes

Added ExpansionPanel and ExpansionPanelList. The implementation
is based on the Material design spec, without enforcing every
facet of it, leaving the developer using this the liberty to
enforced it lower down the widget tree. This decision was made
based on the argument that implementing more of the spec would
reduce flexibility to a point where some design would not be
implementable with this widget anymore.