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

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.

* migrate material to nullsafety

* address review comments

* address review comments

* fix build

* Fix even more unresolved doc references in material

* ++

* ++

https://github.com/flutter/flutter/issues/31931

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

* Instead of changing test I just flipped flag so the test uses the proper slider

* Use Depracated annotation

* Updated depracation notice

* Updated depracation notice again

* Ignore analyze issues

* flutter analyze .

* ignore analyzer

* // ignore: deprecated_member_use

* Ignoring notice

* indentation

* [Slider] Rebase.

* disabled thumb color with alphaBlend of colorScheme surface

* test remove alphablend

* Change rectangular track to how it used to be

* Chaned to adaptive slider

* blank lines
Co-authored-by: Will Larche <larche@google.com>

This reverts commit e71cf1cd.

This PR adds the linux and windows target platform enum values, along with automatically setting the defaultTargetPlatform to the appropriate value on those platforms.

Fixes #31366

* implicit-casts:false in flutter/lib/src/material

* address review comments

* 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.

This reverts commit 421bf647.

Was causing severe breakages in Google.

Update the Slider and RangeSlider to the latest Material spec. This introduces an updated track, updated thumbs, updated tick marks, and a new value indicator shape. The old paddle value indicator shape is also updated so that text scaling works consistently.

* Updates to slider_test.dart

Fixed error that required onChanged.

* Updated slider.dart and slider_test.dart debugFillProperties

Updated slider.dart debugFillProperties to include all properties and slider_test debugFillProperties to test all properties

* Updated Slider onChanged property

* Updated debugFillProperties to ignore testing methods that are null in test

Per feedback from Hans/Anthony on Flutter Material

* Updated spacing in debugFillProperties

Per feedback from Hans

* Updated range_slider.dart and range_slider_test.dart to have DiagnosticProperties tests for all properties

* Updated range_slider.dart and range_slider_test.dart per feedback

Preventing null labels from creating an error.

Added made RangeLabels and RangeValues constants in instantiation of Range Slider.

Fixed spacing.

* Updates to start and end labels in diagnostic property tests

Updated per feedback from @clocksmith