New M3 Demo App for Master Channel

[QuncCccccc]

This PR creates a new Material 3 demo app in the experimental directory. The app contains all the updated M3 components in the Flutter master channel.

Pre-launch Checklist

• [x] I read the [Flutter Style Guide] recently, and have followed its advice.
• [x] I signed the [CLA].
• [x] I read the [Contributors Guide].
• [ ] I updated/added relevant documentation (doc comments with ///).
• [x] All existing and new tests are passing.

[domesticmouse]

Note, this PR is blocked on #1379

[hannah-hyj]

Added textfields too

[domesticmouse]

Some code style issues will be more obvious once the CI pipeline is integrated. It'll pick up things like single vs double quoted strings.

[QuncCccccc]

Some code style issues will be more obvious once the CI pipeline is integrated. It'll pick up things like single vs double quoted strings.

Should I give a larger value of the line length to the formatter instead of the default 80, so that some code can fit in one line? like flutter format -l100 <file>

[domesticmouse]

Please add this project to flutter_ci_script_master.sh to kick in the master CI pipeline.

[QuncCccccc]

Please add this project to flutter_ci_script_master.sh to kick in the master CI pipeline.

Just added. Please let me know if there's any problems.

[domesticmouse]

Please add this project to flutter_ci_script_master.sh to kick in the master CI pipeline.

Just added. Please let me know if there's any problems.

Looks like the CI pipeline spat the dummy:

== Testing 'experimental/material_3_demo' on Flutter's master channel ==
~/work/samples/samples/experimental/material_3_demo ~/work/samples/samples
Running "flutter pub get" in material_3_demo...                  2,007ms
Analyzing material_3_demo...

warning - analysis_options.yaml:1:10 - The include file '../analysis_options.yaml' in '/home/runner/work/samples/samples/experimental/material_3_demo/analysis_options.yaml' can't be found when analyzing '/home/runner/work/samples/samples/experimental/material_3_demo'. - include_file_not_found

I think you'll find it needs to be ../../analysis_options.yaml. This is a result of moving the example into the experimental directory.

[domesticmouse]

Master CI failure:

== Testing 'experimental/material_3_demo' on Flutter's master channel ==
~/work/samples/samples/experimental/material_3_demo ~/work/samples/samples
Running "flutter pub get" in material_3_demo...                  1,977ms
Analyzing material_3_demo...

   info - lib/component_screen.dart:260:23 - Prefer const with constant constructors. - prefer_const_constructors
   info - lib/component_screen.dart:285:23 - Prefer const with constant constructors. - prefer_const_constructors
   info - lib/component_screen.dart:312:23 - Prefer const with constant constructors. - prefer_const_constructors
   info - lib/component_screen.dart:825:44 - Avoid annotating types for function expression parameters. - avoid_types_on_closure_parameters

4 issues found.

[domesticmouse]

LGTM, feel free to land when the other CI steps turn green. Alternatively, I can land this the next time I take a pass through the stack.