Update samples to use repo analysis options, Fix sample templates and a ton of analyzer issues (#77868)

* Add 'See also' to cupertino library

* Add snippets to CupertinoApp

* Add CupertinoPageScaffold samples

* Revert "Add CupertinoPageScaffold samples"

This reverts commit 01b0adf351f0320af7835551102d62e3416f0eab.

* Revert "Revert "Add CupertinoPageScaffold samples""

This reverts commit 0af506237a16f7fec5f3744a9bd015a511a15f72.

* Add CupertinoNavigationBar sample

* Tweak CupertinoPageScaffold sample

* Don't use Material in cupertino samples

* Fix colors

* Fix capitalization
Co-authored-by: Shi-Hao Hong <shihaohong@google.com>

* Apply suggestions from code review
Co-authored-by: Shi-Hao Hong <shihaohong@google.com>

* Add comment about backgroundColor
Co-authored-by: Shi-Hao Hong <shihaohong@google.com>

This reverts commit 9b56241e.

This reverts commit 1f0df545.

* Remove nullOk from cupertino color resolution

* Add CupertinoDynamicColor.maybeResolveFrom

* Remove CupertinoDynamicColor.maybeResolveFrom again

Adds MediaQuery.maybeOf to replace calling MediaQuery.of(context, nullOk: true), and removes the nullOk parameter. Also changes MediaQuery.of to return a non-nullable value, and removes many instances of the ! operator, reducing the possible places where a null dereference could occur.

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

* add key to constructors of public widgets

* fix a test

* fix a test

* 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

Fix a bug in CupertinoTextField where resizeToAvoidBottomInset didn't work.

Remove the additional top padding from CupertinoPageScaffold's MediaQuery when the navigation bar is opaque (as the padding was already consumed by the navigation bar).

Related Issue: #29136

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

- Add override of border color of CupertinoNavigationBar
- Add background color to CupertinoPageScaffold

Let translucent Cupertino bars have its scaffold children automatically pad their heights - second try (#13440)

* Let translucent Cupertino bars have its scaffold children automatically pad their heights (#13194)

* Let lists automatically add sliver padding from media query. Translucent nav and tab bars leave behind media query paddings in scaffolds.

* tests

* const lint

* Rename base abstract class to generalized ObstructingPreferredSizeWidget

* review

* More docs and comments from #13317

Revert "Let translucent Cupertino bars have its scaffold children automatically pad their heights (#13194)" (#13317)

This reverts commit 5c4ffa13.

* Let lists automatically add sliver padding from media query. Translucent nav and tab bars leave behind media query paddings in scaffolds.

* tests

* const lint

* Rename base abstract class to generalized ObstructingPreferredSizeWidget

* SafeArea

* AnimatedSafeArea

* AppBar test

* Apply feedback

* Refactor CupertinoScaffold

* Rename rootTabPageBuilder to tabBuilder

* fix tab transparency padding

* add a CupertinoTab

* Add default background color

* Add a bunch of examples

* A bunch of tests

* Refactor CupertinoScaffold

* Rename rootTabPageBuilder to tabBuilder

* fix tab transparency padding

* Add default background color

* review notes

* fix test

* review

* Rename CupertinoTab to CupertinoTabView

* remove final ; in sample code for analyzer

* Refactor CupertinoScaffold

* Rename rootTabPageBuilder to tabBuilder

* fix tab transparency padding

* Add default background color

* review notes

* fix test