* Update README to respect GitHub site theme

GitHub recently added support for specifying an alternate appearance when the site is using a dark theme [(see the changelog)](https://github.blog/changelog/2022-05-19-specify-theme-context-for-images-in-markdown-beta/). I've implemented this here with download links from https://flutter.dev/brand.

* Change alt text

This reverts commit 180566f2.

* add actionsPadding to dialog theme and refactor

* fix typo

* remove trailing spaces

* update docs

* use correct actions padding for dialogs

* remove trailing spaces

* Update dialog_theme.dart

* Update packages/flutter/lib/src/material/dialog.dart
Co-authored-by: Taha Tesser <tessertaha@gmail.com>
Co-authored-by: Taha Tesser <tessertaha@gmail.com>

0d1057ef7 [Impeller] Control GL error checking and tracing via GN options. (flutter/engine#33734) (#105086)

In https://github.com/flutter/flutter/pull/103771, we rolled
dependencies in Flutter, which triggered an update of package:coverage
to v1.3.1. The new version includes
https://github.com/dart-lang/coverage/pull/370 in which two deprecations
landed:

* The `Resolver` default constructor was deprecated and replaced with
  the `Resolver.create` static factory method, which unfortunately
  happens to be async.
* The `packagesPath` parameter to `HitMap.parseJson`, which takes the
  path to the `.packages` file of the package for which coverage is to
  be collected, was deprecated. This parameter was replaced with
  `packagePath` in https://github.com/dart-lang/coverage/pull/370 which
  was part of the overall deprecation of the .packages file in Dart
  itself https://github.com/dart-lang/sdk/issues/48272. The overall goal
  being that end-user code shouldn't need to know about implementation
  details such as whether dependency information is stored in a
  .packages file or a package_info.json file, but rather use the
  package_config package to obtain the package metadata and perform
  other functions such as resolving its dependencies to filesystem
  paths. packagesPath was replaced by packagePath, which takes the path
  to the package directory itself. Internally, package:coverage then
  uses package_config to do the rest of the package/script URI
  resolution to filesystem paths.

This migrates off the deprecated `packagesPath` parameter to the
replacement `packagePath` paramter.

Issue: https://github.com/flutter/flutter/issues/103830

* more const immutable classes

* more const constructors in dev/ and examples/

This reverts part of the change made in #103456 to expose a debug check for subclasses of ChangeNotifier to avoid code duplication. Instead of making debugAssertNotDisposed a public instance function, it is now a public static function. It makes it harder to call, slightly, but it means that everyone who implemented ChangeNotifier instead of extending it doesn't get broken.