* Reland "Live image cache" (#51441)

This reverts commit 419a2853.

* Make evict safer

* Revert "Live image cache (#51249)"

This reverts commit e2dcdb60.

* fix tests for other commit

* Revert "Revert "Live image cache (#50318)" (#51131)"

This reverts commit 2f09d601.

* Fix eviction of a pending image

This reverts commit 1602be6a.

Track images available on screen

This PR modifies the existing API docs samples to use DartPad so that all of the samples are now interactive apps on the API docs site.

It also removes the restriction for the max width of the description area so that the dartpad region can expand horizontally.

I updated the first paragraph on the API docs to indicate that Flutter is more than just mobile now (same text as the README.md at the top level).

I modified a few of the examples so that they looked nicer, and fit better on the page.

I added the sample description text above each DartPad instance, since that often defines the context of the example.

I removed animations and images when they were redundant with the sample content. There were a few that made sense to keep, so I did.

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

See https://github.com/flutter/flutter/issues/37423

* Add images and update examples for top widgets:

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

Tickers being disabled and re-enabled can cause the
condition of a synchronous notification happening after
image frames have been delivered, which is valid in that
case. As such, this removes the assert.

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

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

The current API was broken in that you registered multiple
callbacks at once, but when you removed listeners, only the
primary listener was used to determine what was removed.
This led to unintuitive cases where the caller could get
unexpected behavior.

This updates the API to add and remove listeners using
a newly introduced [ImageStreamListener] object, a value
object that has references to the individual callbacks
that may fire.

flutter/flutter#24722
flutter/flutter#32374
flutter/flutter#32935

* use null aware operators

* rollback changes about null-aware operator

* disable lint prefer_is_not_empty

Make FlutterError objects more structured so they can be displayed better in debugging tools such as Dart DevTools.

* Adding linking between higher and lower level classes in the API Docs. ref:#22859

* Fixed links between classes.

* add trailing commas on list/map/parameters

* add trailing commas on Invocation with nb of arg>1

* add commas for widget containing widgets

* add trailing commas if instantiation contains trailing comma

* revert bad change

Fix the spelling errors in the dartdocs for the framework.

There are no functionality changes here, just documentation fixes.

This converts existing ## Sample code samples to {@tool sample}...{@end-tool} form.

Also:
1. Fixed a minor bug in analyze-sample-code.dart
2. Made the snippet tool only insert descriptions if the description is non-empty.
3. Moved the Card diagram to before the code sample.

* Update/add missing period to doc

* Added a filterQuality parameter to images.

* Removed this break by accident.

* Modified the test case to check the filterQuality

* Update packages/flutter/lib/src/rendering/image.dart
Co-Authored-By: namanix <namanix@gmail.com>

* Update packages/flutter/lib/src/rendering/image.dart
Co-Authored-By: namanix <namanix@gmail.com>

* Update packages/flutter/lib/src/rendering/image.dart
Co-Authored-By: namanix <namanix@gmail.com>

* Update packages/flutter/lib/src/widgets/image.dart
Co-Authored-By: namanix <namanix@gmail.com>

* Update packages/flutter/lib/src/widgets/image.dart
Co-Authored-By: namanix <namanix@gmail.com>

* Update packages/flutter/lib/src/rendering/image.dart
Co-Authored-By: namanix <namanix@gmail.com>

* Update packages/flutter/lib/src/rendering/image.dart
Co-Authored-By: namanix <namanix@gmail.com>

* Added documentation for the new parameter and corrected some space issue's

* Future<void> main

* Future<void>.delayed

* prefer_void_to_Null

* address review comments