This relands flutter/flutter#33163 with a fix to the integration_ui test.

- Fixed extentInside calculation in ScrollMetrics
- Added asserts to extentInside getter, as well as ScrollPosition.applyContentDimensions to enforce minScrollExtent <= maxScrollExtent
- Added padding to ScrollbarPainter, updated implementation. Took care of some edge cases.
- Changed some scroll bar constants on Cupertino side.

Fixed an issue with a DropdownButton crashing when a style was used that didn't include a fontSize.

Switch from building Runner.vcxproj to Runner.sln on Windows, to allow
for multiple-project builds (e.g., separate plugin projects).

This adds two new builders to the `Image` class:

* `frameBuilder`, which allows callers to control the widget
  created by an [Image].
* `loadingBuilder`, which allows callers fine-grained control
  over how to display loading progress of an image to the user.

`FadeInImage` can be simplified by migrating to the new API.
This is done in a follow-on commit.

https://github.com/flutter/flutter/issues/32374

This reverts commit 52ae9968.

Rather than hard-coding a set of locations to check, use vswhere (which
is installed by VS 2017 and later), and construct the vcvars64.bat path
relative to that. This will allow Windows builds to work without special
configuration for people who have VS installed at a custom path.

Also adds error logging with different messages for each failure point,
so that rather than the not-very-informative 'failed to find
vcvars64.bat' message, the failure will provide feedback about what to
do.

This is an interim solution; later this will be replaced by a
VisualStudio class with associated validator to match the structure of
the other toolchains.

Fixes #33249

Invoking msbuild with runInShell makes handling path escaping more
error-prone, and substantially increases the chances of running into
maximum path limits. This replaces the direct call with a .bat wrapper
that calls vsvars64.bat then msbuild, and uses relative paths within the
script to keep command lengths short.

Fixes https://github.com/flutter/flutter/issues/32792

This will fix a failure in dev/bots/analyze-sample-code.dart when using
the tip of tree Dart SDK.

This reverts commit faec4ca3.

This reverts commit 841286d6.

* Deprecates `BinaryMessages` in favor of a default instance of `BinaryMessenger`, called `defaultBinaryMessenger`
* Platform channels use the `defaultBinaryMessenger` for their binaryMessenger default argument.

See https://github.com/flutter/flutter/issues/31691

Replacing the algorithm for finding the first focusable item in the focus tree. Somehow it was a kind of gibberish before, and really didn't work or make sense.

Co-authored-by: Miguel Lemos <miguelslemos@gmail.com>

* 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

This also fixes up some indentation in some
bulleted lists.

https://github.com/dart-lang/dartdoc/issues/1969

Splits Xcode validation out of the iOS validator and into a stand-alone
validator, and groups the CocoaPods validator with that top-level
validator instead of the iOS validator. iOS now validates only the
iOS-specific tools (e.g., ideviceinstaller).

Reorganizes many of the associated clases so that those that are used by
both macOS and iOS live in macos/ rather than ios/. Moves some
validators to their own files as part of the restructuring.

This is the macOS portion of #31368

Updates documentation and non-public API to use American spellings for
consistency with the rest of the codebase.

No changes to behaviour... other than how it's spelt.

Corects a bnuch of typeos throuhgout teh Fluter codebsae.

Made use of the `misspell` tool:
https://github.com/client9/misspell

Adds a new macosPrefix, which serves the same purpose as iosPrefix but
for macOS plugins.

It is not yet used by the tooling, but this allows for plugins to start
to be written using it in preparation for tooling support for plugins.

Part of #32718

* Implement ExpandIcon custom color, expandedColor, and disabledColor

* Update to use pumpAndSettle instead of hard-coded duration

* Update colors to unfocused state, added dark mode test to active state

* Fix Colors.white30 doc opacity value

* Add links to Material Design specifications to color, expandedColor and disabledColor

* Update API docs to reference dark theme material page