* Adding snackbar theme data width field

* Whitespace formatting

* Update docstrings

* version update

* tidy up

* Revert auto text formatting

* Text formatting

* Remove whitespace

* Test tidy

* Whitespace fix

* y Please enter the commit message for your changes. Lines starting

* whitespace

* test fixes

* de-British-ification

* comment modification

This reverts commit b3aba4d9 because it breaks Google tests.

* Migrate more Material framework tests to null safety.

This reverts commit adc5f26b.

This reverts commit 48f1a0a8.

* 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

* Allow for customizing Snackbar's content TextStyle in its theme

* Address PR feedback

* Fix analyzer issues

* Address more PR feedback

This PR introduces a number of changes and improvements to snack bars. This includes the ability to specify:

floating style of snack bars that adhere to the updated Material spec
elevation and shape on the SnackBar itself instead of relying on fixed values
a snackBarTheme as part of ThemeData which allows you to customize all of the above on an app-wide level.
This PR is includes the changes from #21484 as well as additional fixes and modifications. Thanks to @NikoYuwono for providing these changes and getting this off the ground!