This changes the behavior of text fields, Material buttons, and Chips so that if they are disabled they lose focus. Before this change, it was possible to disable a control and then use focus traversal to reach it anyhow, and in the case of text fields, enter text into a disabled field.

Fixes #33985

I noticed that we were pretty inconsistent with the way that we checked the value of clipBehavior in the framework, so I normalized the usages and updated docs where necessary.

This is a breaking change if you used to pass null explicitly to FlatButton, OutlineButton or RaisedButton constructors, expecting to get Clip.none. It will now assert if you do that. Existing implementations that pass null implicitly by not specifying clipBehavior won't need to change their call sites. It always implicitly defaulted to Clip.none before, and it will continue to do that, it's only places where it was explicitly set to null in order to get the implicit default that it will fail.

Add an autofocus parameter to widgets which use Focus widget internally, and update related docs.

This will allow developers to request that a particular widget be automatically focused when shown.

Re-land "[Material] Support for hovered, focused, and pressed border color on `OutlineButton`s" (#35278)

* outline border implements material state property

Revert "[Material] Support for hovered, focused, and pressed border color on `OutlineButton`s (#34872)" (#35276)

This reverts commit 3f941599.

* outline border implements material state property

* Support for stateful text colors in buttons

* Add color and a11y tests for buttons

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.

Previously, a disabled floating action button always had zero
elevation, which looks dumb.

This also fixes the issue whereby highlightElevation was not honoured
on floating action buttons.

This also fixes an issue I found during testing whereby setState was
being called during build when onHighlightChanged fired due to
onPressed becoming null while a gesture is ongoing (which triggers an
onTapCancel synchronously during build).

This reverts commit 80f80ab0.

For G3 Roll:

* Revert "MaterialButton must honor its minWidth and height parameters (#22919)"

This reverts commit a0233233.

* Revert "Update uses of ButtonTheme.bar: pass along the current Theme's colorScheme (#22827)"

This reverts commit 655bf6a2.

* Revert "ButtonTheme.of().colorScheme defers to Theme (#22880)"

This reverts commit a590940e.

* Revert "Bring TextTheme into alignment with the current Material spec (#22330)"

This reverts commit 8bfb4b3e.

* Revert "Added ColorScheme, updated ThemeData, ButtonTheme, material buttons (#22013)"

This reverts commit eea3465a.

* Manual adjustments to fix reversion issues.

Introduce an overall material "color scheme" and to make it possible to redefine how a component's visual properties bind to the color scheme and to the existing material Theme.

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* lint unnecessary_new on samples

* fix tests

Closes #3188

This reverts commit 8de0e15e and
updates the goldens versoin.

This requires https://github.com/flutter/flutter/pull/20751 to
land first.

This fixes #20483 by letting InkWell do its own clipping.

PathOp.intersect is not used because we have too many unit tests that rely on clipping (e.g., paints..clipXXX()..drawCircle())

The goldens are updated due to small AA changes of the additional clipPath.

- remove an //ignore that is no longer needed
- fix some intrinsic methods that used the API incorrectly (shouldn't affect correctness but should make things a tiny bit more efficient)
- add some asserts to help track down bugs quicker
- update a TODO to point to the currently relevant bug
- fix some indenting
- improve the naming of some privates to improve readability

This fixes https://github.com/flutter/flutter/issues/18057

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit 989f5741.

`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.

This attempts to apply some of what we learnt from UX studies, namely
that people wonder how to add multiple children to widget that take
one child.

https://github.com/flutter/flutter/issues/11992

This modifies the MaterialButton to expand vertically to fit the size of the contained child, no matter what the child widget is. It tries to be as close as possible to the minHeight constraint.

Also updated some doc comments to have headers (extra blank line after first sentence), and to wrap at 80 cols.

Addresses #12311