## 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 painting and rendering libraries.

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after null safety has been made the default, these comments were largely fragile, in that it was easy for them to get out of date, and not be accurate anymore anyhow.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/134991
- https://github.com/flutter/flutter/pull/134992
- https://github.com/flutter/flutter/pull/134994

## Tests
 - Documentation only change.

Fix `CastError` in `StadiumBorder.lerpTo` and  `StadiumBorder.lerpFrom` when using `BorderRadiusDirectional` (#114826)

* Fix casting in StadiumBorder lerp

* Add tests

* Fix made-up names

This reverts commit b3aba4d9 because it breaks Google tests.

Use `curly_braces_in_flow_control_structures` for `foundation`, `gestures`, `painting`, `physics` (#104610)

* Use `curly_braces_in_flow_control_structures` for `foundation`

* Use `curly_braces_in_flow_control_structures` for `gestures`

* Use `curly_braces_in_flow_control_structures` for `painting`

* Use `curly_braces_in_flow_control_structures` for `physics`

* fix comments

* remove trailing space

* fix TODO style

* migrates lib/foundation and lib/widgets

* migrates lib/painting and lib/material

* migrates lib/cupertino, lib/gestures, lib/services, lib/semantics and lib/rendering

* fixes failing tests

* migrates test/

* improves hashing of lists

* migrate painting to nullsafety

* address review comments

* 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

* 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

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

This cleans up lerp, lerpFrom, lerpTo, and scale methods, and their
documentation.

Fixes https://github.com/flutter/flutter/issues/12377.

In order to allow chips to be properly drawn when they expand in size (without
using IntrinsicHeight), I needed a BoxDecoration shape that would be dependent
upon the rendered height of the widget. This seemed to be pretty generally
useful, so I added a new ShapeDecoration called StadiumBorder. It uses the
minimum dimension to adjust the BorderRadius of a rounded rect in the shape
decoration.

I also converted some uses of BoxShape to be case statements, updated the
chips to use the StadiumBorder decoration, and updated some of the metrics to match
the Material spec, as well as implementing lerping to and from StadiumBorder.

* enable lint prefer_const_constructors_in_immutables

* remove LabeledGlobalKey._