This follows https://github.com/flutter/flutter/pull/59364 and cl/319911104

FittedBox is still default to hardEdge clip as new FittedBox is added to Google very quickly. Let's first roll other part of changes into Google first.

* Revert "Revert "Add clipBehavior to widgets with clipRect (#55977)" (#58344)"

This reverts commit 1d395c5e.

* Add missed Overflow

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

This reverts commit cd593dae.

* Add clipBehavior to RenderFlex

* Add clipBehavior to FittedBox

* Add clipBehavior to Flex and FittedBox

* Add clipBehavior to UnconstrainedBox

* Add clipBehavior to Stack and Wrap

* Add clipBehavior to TextEditable

* Add clipBehavior to ListWheelScrollView

* Add clipBehavior to SingleChildScrollView

* Add clipBehavior to RenderViewportBase's widgets

Those widgets are NestedScrollView and ShrinkWrappingViewport.

* Fix tests

* Remove enum Overflow and fix typo

* Remove clipToSize

* Analyze fix

* Remove Mixin and other small fixes

* Fix tests and respect Stack's default clipBehavior

* Add Overflow back to make it non-breaking

* Restore clipBehavior to make it non-breaking

* Small fixes

* Fix rebase

* replace simple Container(w & h) with SizedBox

* address review comments

* address review comments

* 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

* add missing trailing commas

* add more missing trailing commas

* add more and more missing trailing commas

* Re-enable const

* add trailing commas on list/map/parameters

* add trailing commas on Invocation with nb of arg>1

* add commas for widget containing widgets

* add trailing commas if instantiation contains trailing comma

* revert bad change

* fix some bad indentations

* remove suspicious line

* 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.

Various improvements (in particular a new painting fuzzer) to the text manual test.

Some additional documentation.

A fix to Stack to remove an LTR bias: make unpositioned children apply "alignment".

Some more debugging information on RichText and Text.

A fix to the flutter tool to not crash when an RPC call throws an exception.

Unlike FractionalOffset, Alignment uses the center as the zero of the
coordinate system, which makes the RTL math work out much cleaner.

Also, make FractionalOffset into a subclass of Alignment so that clients
can continue to use FractionalOffset.

Notice that the default alignment for Stack needs to know the
directionality.

This patch adds Positioned.directional and PositionedDirectional. The
former is useful when you already know the TextDirection. The latter is
useful when you want to use the ambeient Directionality.

Fixes #11390

backgroundColor -> color
backgroundImage -> image
BackgroundImage -> DecorationImage

The enum is called StackFit, so the property name "fit" makes more sense.

Also:

 * Add three explicit sizing modes to Stack for non-positioned
   children: loose, expand, and passthrough. (All three are used.)

 * Fix a bug whereby layers would try to paint in the same frame as
   they were removed from layout (but not detached).

 * Fix a bug whereby Offstage wasn't properly marking the parent dirty
   when changing its sizedByParent flag.

 * Explicitly make Overlay expand non-positioned children.

 * Explicitly have InputDecoration pass through the constraints from
   its Row to its Stack children.

Added a flag that instructs Stack how to deal with overflowing
children: they can either be clipped or not.

This makes it possible to substitute 'flutter run' for 'flutter test'
and actually watch a test run on a device.

For any test that depends on flutter_test:

1. Remove any import of 'package:test/test.dart'.

2. Replace `testWidgets('...', (WidgetTester tester) {`
      with `testWidgets('...', (WidgetTester tester) async {`

3. Add an "await" in front of calls to any of the following:
    * tap()
    * tapAt()
    * fling()
    * flingFrom()
    * scroll()
    * scrollAt()
    * pump()
    * pumpWidget()

4. Replace any calls to `tester.flushMicrotasks()` with calls to
   `await tester.idle()`.

There's a guarding API that you can use, if you have particularly
complicated tests, to get better error messages. Search for
TestAsyncUtils.