Adds a default title to the Title widget, fixes #6802.

Diagnostics object is.

Fix a bunch of obvious RTL bugs from code inspection.

* Make an app's supported locales configurable

* Added an supportedLocales.isNotEmpty assert

* WidgetsApp no longer const because supportedLocales.isNotEmpty

* updated per review feedback

* tweaked dartdoc to restart the build

* updated per review feedback

* Updated per review feedback

This patch just fixes the next and previous buttons to be in the proper
place. There might be other issues with the DatePicker, but this one was
obvious.

See #11377

Fixes #11855

Fixes #11868

Fixes #11379

Most of the framework widgets should work in terms of EdgeInsetsGeometry
rather than EdgeInsets so that their clients can supply directional
insets.

Fixes #5215

Fixes #11381

Fixes #11373

Fixes #11374

When scrolling vertically, the scrollbar is on the left in RTL.

Fixes #11369

Fixes #11358

* Notify the completer after the close animation completes on the snackbar

* Review comments

* Fix tests and analyzer warnings

* Fix analyzer warnings

* 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.

* refactor to ensureAction + some related doc fixes

* Update docs for markNeedsSemanticsUpdate

* rewording

* rewording

* ensureAction test

* ensureAction test

* ensureAction test

* more tests

* refactor to allways reset node

* tiny fixes

* more test

* doc fixes

* one more test

* review comments

* Properly update semantics when Material/Cupertino Slider are disabled

* whitespace fix

* fix style

Bare bones widget inspector support.

Toggle the widget inspector from the flutter tool by pressing 'i'.
When the widget inspector is select mode:
Pointer down to to inspect a widget.
Pointer click to finalize selection of a widget. You can now interact
with the application as you normally would but with the inspected widget
highlighted.
Click the inspect icon in bottom left corner of screen to reactivate
select mode.

when describing non-nullable method arguments.

Some widgets are using closures even if the only values that are
captured are this, context or widget, that can be accessed even from
methods of the State object.

* Let the initial date picker mode be selectable

* Doc for enum

* Add a test

* Add a comment for test

* actually decouple test from setup state

* Wrap the label widget of the Chip in a Flexible. (#11523)

* This allows the Chip to constrain the size of its content after taking into account the space occupied by the avatar and delete icon (if they are present)

* Adding unit tests to evaluate correct size constraints of the Chip widget's label. (#11523)

* Minor change in formatting.

* Adjust function formatting.

* a11y: handle left/right scrolls correctly

* fix keep alive test

* fix scaffold test

* Allow tapping on TabBar indicator to switch tabs

* fix semantics

* review comments

* Adds more customization options to the Chip widget

Includes:
- Custom Tooltip message for the delete button;
- Custom background color for the chip
- Custom delete icon color
- Custom label text style

* Adds missing type annotations to tests and improves documentation.

* Tweaks labelStyle field documentation

Add Diagnosticable base class and documentation