* Make upscaling images opt-in

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

* Avoid including a potentially animated invisible image

* 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

Default `semanticsEnabled` to true for `testWidgets` and fix associated bugs

This updates FadeInImage to use the new Image.frameBuilder
API (added in #33369), to greatly simplify the implementation
of FadeInImage.

This also removes the FadeInImage.placeholderSemanticLabel property.
This property was added in #28799 for the sake of completeness (the bug
it fixed was the lack of any semantic label support in FadeInImage), but a
placeholder is a transient visual artifact, not something that affects the
underlying semantic meaning of the image.

* Future<void> main

* Future<void>.delayed

* prefer_void_to_Null

* address review comments

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

This allows the scheduler library to depend on the services library
and the painting library to depend on the scheduler library without
the services library having to depend on the scheduler library.

While I was at it I also cleaned up some of the binding logic: the
licenses logic can now be overridden (and the test library does so),
and the image cache can now be overridden as well.

* FadeInImage: shows a placeholder while loading then fades in

* fix dartdoc quotes

* license headers; imports

* use ImageProvider; docs; constructors

* _resolveImage when placeholder changes

* address comments

* docs re ImageProvider changes; unsubscribe from placeholder

* rebase

* address comments