* dart fix --apply

* manual fixes

* Add Material 3 support for `TabBar`

* M3 `TabBar` revert fix and tests

This reverts commit 900b3954.

* migrate material to nullsafety

* address review comments

* address review comments

* fix build

This allows us to rationalize the nullability of some of our APIs.
Prior to this we'd end up in a situation where Container assumed that
getClipPath would be non-null but Decoration was ok with return null.

* Fix even more unresolved doc references in material

* ++

* ++

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

* 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

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

Tabs are now padded by 16.0 on the left and right  (used to be 12.0).