Adds Navigator.maybeOf to replace calling Navigator.of(context, nullOk: true), and removes the nullOk parameter. Also changes Navigator.of to return a non-nullable value, and removes many (120!) instances of the ! operator, reducing the possible places where a null dereference could occur.

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.

This reverts commit 81439922.

* migrate some material files to nullsafety

* review

Updated references to the old button classes to the new ones in comments and documentation for classes in the material library. (#62092)

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

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

This PR modifies the existing API docs samples to use DartPad so that all of the samples are now interactive apps on the API docs site.

It also removes the restriction for the max width of the description area so that the dartpad region can expand horizontally.

I updated the first paragraph on the API docs to indicate that Flutter is more than just mobile now (same text as the README.md at the top level).

I modified a few of the examples so that they looked nicer, and fit better on the page.

I added the sample description text above each DartPad instance, since that often defines the context of the example.

I removed animations and images when they were redundant with the sample content. There were a few that made sense to keep, so I did.

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

* address review comments

* Api Samples and Diagrams for the following classes and methods:

  - AlertDialog
  - SimpleDialog
  - SingleChildScrollView
  - showDatePicker
  - RichText
  - InputDecoration
  - Divider
  - StreamBuilder
  - DataTable
  - BottomSheet
    - showBottomSheet
    - showModalBottomSheet

* Update packages/flutter/lib/src/material/divider.dart
Co-Authored-By: Kate Lovett <katelovett@google.com>

* Update packages/flutter/lib/src/widgets/basic.dart
Co-Authored-By: Kate Lovett <katelovett@google.com>

* Update packages/flutter/lib/src/material/data_table.dart
Co-Authored-By: Kate Lovett <katelovett@google.com>

* Update packages/flutter/lib/src/material/bottom_sheet.dart
Co-Authored-By: Kate Lovett <katelovett@google.com>

* Update packages/flutter/lib/src/material/scaffold.dart
Co-Authored-By: Kate Lovett <katelovett@google.com>

* Move animation out of sample

* Remove "widget.size", replace with "60"

* 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

This PR adds TargetPlatform.macOS to the TargetPlatform enum. This allows us to begin implementation of some adaptive UI based on which target platform is desired.

I haven't updated the tests here, that will come in a follow-up PR.

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

* Allow showModalBottomSheet to present bottom sheet that is not dismissible by tapping on the scrim

* Add guards, improve styling and tests for BottomSheet

Fix regression with ModalBottomSheets not responding to changes in theme
after they are shown.