* 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

No code changes, just comments: I spell-checked all the comments in the repo.

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

* Fixed links between classes.

Fix the spelling errors in the dartdocs for the framework.

There are no functionality changes here, just documentation fixes.

Integrate Strut: Add StrutStyle, expose Strut API, wire up strut with dart:ui, Roll engine 31a7f4d..e7eb1c8 (7 commits) (#26332)

Includes a breaking change to dart:ui ParagraphStyle where lineHeight is renamed to height for consistency with TextStyle.