This implements focus and hover handling for Material buttons. It inserts Focus widgets into the tree in order to allow buttons to be focusable via keyboard traversal (a.k.a. TAB traversal), and Listener widgets into the InkWell to allow the detection of hover states for widgets.

Addresses #11344, #1608, and #13264.

* First impl with StopwatchWithZone

* Clean up params and name

* Remove outdated TODO

* Fix style

* Fix a missing param. Add @require

* Fix import meta

* Fix code style

* Add missing require. Fix comment style.

* Fix code style

* Fix code style

* 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

* the onStart callback will report the location of the pointer where it wins the gesture arena by default instead of the pointer down location. Fixes all tests related to changing this default value.

This reverts commit 08538f91.

* Adds start behavior option to the drag gesture recognizer and makes it the default option when a drag gesture recognizer is created. Also fixes all the tests to work correctly with the new default behavior.

* Future<void> main

* Future<void>.delayed

* prefer_void_to_Null

* address review comments

* 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.

Adding some tests for onTapDown and onTapCancel for the InkWell, as suggested in post-submission comments by @Hixie in #16190.

Also, added those to the diagnostic output.

This is done to keep in place the workaround we have for rectangular material
where PhysicalModel skips the saveLayer call.

This reverts commit d9ef7df9.

0672055a changed the Material widget to
always use Paths for representing the outline.
These paths are later used for clipping and drawing a shadow.
This changed introduced a performance regression, see:
https://github.com/flutter/flutter/issues/14403

We did not expect a path that is a rounded rectangle to be less
performant than a rounded rectangle, as Skia should be able to tell the
path is just a rounded rectangle.
Until we find a solution for this regression, we keep using RRect when
we can represent the shape with it.

For backward compatibility we keep supporting specifying the shape as a
combination of MaterialType and borderRadius, and we just use that as a
default when shapeBorder is null.

To cleanup the implementation if shapeBorder was not specified we just
translate the specified shape to a shapeBorder internally.
I benchmarked paint, layout and hit testing, with the specialized shape
clippers vs. the equivalent path clippers and did not see any
significant performance difference.

For testing, I extended the clippers/physicalShape matchers to match either the
specialized shape or the equivalent shape.

Fixes #13743 
Fixes #12379
Follow-up to #13745

Also adds an option to hide gestures introduced by `InkWell` and `InkResponse` from the semantics tree (see also `GestureDetector.excludeFromSemantics`).

Fixes #11855

* AutomaticKeepAlive

A Widget that listens for notifications from widgets that don't want to die.

* Automatically wrap SliverList and SliverGrid children in AutomaticKeepAlive widgets

* Fixes for review comments

* Provide haptic/acoustic feedback for tap & long-press on Android

* review comments

* fixed example code

* review comments

* comment fix

The demo of the SimpleDialog had some useful code that should really be part of
the framework. This patch extracts it into a SimpleDialogOption widget.

Remove debugCheckHasScaffold because it is unused.

Also, add tests for InkWell, SimpleDialog, and other widgets.