## Description

This removes all of the comments that are of the form "so-and-so (must not be null|can ?not be null|must be non-null)" from the cases where those values are defines as non-nullable values.

This PR removes them from the material library.

This was done by hand, since it really didn't lend itself to scripting, so it needs to be more than just spot-checked, I think. I was careful to leave any comment that referred to parameters that were nullable, but I may have missed some.

In addition to being no longer relevant after null safety has been made the default, these comments were largely fragile, in that it was easy for them to get out of date, and not be accurate anymore anyhow.

This did create a number of constructor comments which basically say "Creates a [Foo].", but I don't really know how to avoid that in a large scale change, since there's not much you can really say in a lot of cases.  I think we might consider some leniency for constructors to the "Comment must be meaningful" style guidance (which we de facto have already, since there are a bunch of these).

## Related PRs
- https://github.com/flutter/flutter/pull/134984
- https://github.com/flutter/flutter/pull/134992
- https://github.com/flutter/flutter/pull/134993
- https://github.com/flutter/flutter/pull/134994

## Tests
 - Documentation only change.

* dart fix --apply

* manual fixes

* fix deprecated_new_in_comment_reference for `material` library

in a future version of the SDK, these will be flagged, fix them now

* Update pubspec.yaml

* migrate some material files to nullsafty

* address review comments

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

* implicit-casts:false in flutter/lib/src/material

* address review comments

* 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

* make BuildContext.{ancestorStateOfType,ancestorRenderObjectOfType,rootAncestorStateOfType} generic

* make BuildContext.inheritFromWidgetOfExactType generic

* make BuildContext.ancestorInheritedElementForWidgetOfExactType generic

* make BuildContext.ancestorWidgetOfExactType generic

* fix snippet

* bump scoped_model on temp version

* update names

* Revert "bump scoped_model on temp version"

This reverts commit d1fcbba028cdb07f44738d1652391692d1ea5ec0.

* address review comments

* fix ci

* address review comments

* repeat the deprecation notice

* fix uppercase

* use of recommanded deprecation syntax

* address review comment

-* Inserted an `IconTheme` widget under `CupertinoTheme` to provide a default icon color when using `CupertinoTheme`.
* Changed `CupertinoTheme` to a `StatelessWidget`, to match the implementation of `Theme`
* Changed the nesting order of `Theme`'s sub widgets, to let `Theme.iconTheme` take precedence, so that `Theme`'s behavior is kept as is.

* 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

This reverts commit 80f80ab0.

For G3 Roll:

* Revert "MaterialButton must honor its minWidth and height parameters (#22919)"

This reverts commit a0233233.

* Revert "Update uses of ButtonTheme.bar: pass along the current Theme's colorScheme (#22827)"

This reverts commit 655bf6a2.

* Revert "ButtonTheme.of().colorScheme defers to Theme (#22880)"

This reverts commit a590940e.

* Revert "Bring TextTheme into alignment with the current Material spec (#22330)"

This reverts commit 8bfb4b3e.

* Revert "Added ColorScheme, updated ThemeData, ButtonTheme, material buttons (#22013)"

This reverts commit eea3465a.

* Manual adjustments to fix reversion issues.

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* lint unnecessary_new on samples

* fix tests

This adds links to the already existing animated diagrams in the asset-for-api-docs repo.

It was causing problems rolling Flutter into Fuchsia