* Set default borderRadius to none in ClipRRect

* add tests

* Adds a new parameter bool opaque to MouseRegion
* The same to RenderMouseRegion and AnnotatedRegionLayer
* Add findAnnotations to Layer 

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.

This fixes the mouse hover code to not schedule frames with every mouse move.

Before this, it would schedule a post frame callback, and then schedule a frame immediately, even if there was nothing that needed to be updated. Now it will schedule checks for mouse position updates synchronously, unless there's a new annotation, and skip scheduling a new frame in all cases. It has to be async in the case of a new annotation (i.e. a new MouseRegion is added), since when the annotation is added, it hasn't yet painted, and it can't hit test against the new layer until after the paint, so in that case it schedules a post frame callback, but since it's already building a frame when it does that, it doesn't need to schedule a frame.

The code also used to do mouse position checks for all mice if only one mouse changed position. I fixed this part too, so that it will only check position for the mouse that changed.

This reverts commit 6ad88bd5.

* Create 'center' template

* Minor improvements to framework documentation.

* maybePop documentation fix

* Mark some flutter_test arguments required.

Without these set, we get a crash.

* Minor correction to ListView docs

The Text in the Transform.scale example is "Bad Ideas", which could be confusing as example code. This PR replaces it with something more random.

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.

- Splits on{Enter,Hover,Exit} from Listener to MouseRegion. Deprecated API is kept for compatibility.
- Splits on{Enter,Hover,Exit} from RenderPointerListener to RenderMouseRegion.

* Add images and update examples for top widgets:

  - scaffold
  - text field
  - image
  - text
  - row
  - column
  - stack

* Fixed assets embedding

* ++

* Completed snippet audit

* Analyzer

* Added some Widgets of the Week to documentation: AspectRatio and AnimatedIcon.

Reland "Text inline widgets, TextSpan rework (#30069)" with improved backwards compatibility (#34051)

This reverts commit 14414f35.

This reverts commit 86862c1e.

* Merge in changes for inline widgets

* Make analyzer happy, fix tests

* Fix analyzer

* Add missing doc

* Docs on RichText

* Fix analyzer some more

* Remove whitespace at end of line

* Update goldens

* Text fixes

* Analyzer

* Adding sample and animation for Flow widget

* Updated dart templates for layout in API docs

* Updated the sample code for a clearer example.

* make clean

* AnimatedList
* Flexible
* Draggable
* ValueListenableBuilder

I recently added some code to keep hover events from being propagated when a mouse wasn't attached. While that works, there are times when it can fire callbacks during the building of other components, since they can now be called from detach/attach. This is not ideal, since it will assert then. This changes the code so that it won't update the annotations during attach/detach, but also won't push the annotation layer unless a mouse is connected, achieving the same result as before, but with better semantics.

The basic problem is that in the detach for RenderPointerListener, it would detach the annotation, which could cause onExit to be called on the annotation, since the widget was disappearing under the mouse, and thus needs to receive an onExit, but that onExit might be (and probably will be) calling setState, which marks the owning widget as needing to be built, sometimes when it already has been.

The fix creates a new _ListenerElement that overrides activate and deactivate in order to tell the render object ahead of the detach that it might be detached, and so the onExit gets called before the detach instead of during it.

In addition, I now avoid scheduling more than one check for mouse positions per frame.

Add `textWidthBasis` param to Text to allow calculating width according to longest line.

This reverts commit 323108ff due to weird engine dependency bug

Add `textWidthBasis` param to Text to allow calculating width according to longest line.

## Description

Make `_RenderCustomClip`'s `clipBehavior` non-final so we can update it during `updateRenderObject`. This will support `clipBehavior` changes in hot reload.

## Related Issues

Fixes #30863

## Tests

I added the following tests:

* ClipRect updates clipBehavior in updateRenderObject
* ClipRRect updates clipBehavior in updateRenderObject
* ClipOval updates clipBehavior in updateRenderObject
* ClipPath updates clipBehavior in updateRenderObject
* PhysicalModel updates clipBehavior in updateRenderObject
* PhysicalShape updates clipBehavior in updateRenderObject

## Description

Clarify that ClipRect can be added to ensure that CustomPainter will be drawing within bounds.

## Related Issues

https://github.com/flutter/flutter/issues/31202