New M3 Demo App for Master Channel (#1378)

* Added components

* Added test

* Added README

* Run flutter format

* Added all the updated components and tests

* Added README file

* Update README.md

* Add textfields to M3 demo app

* move textfield to exprerimental/

* Update component_screen_test.dart

* Fixed comment: changed sdk version

* Changed all double quotes to single

* Added trailing comma, changed all private fields to public except private state classes

* Added enum for screen selection

* Removed comment for material_3_demo

* Added experimental m3 demo app to master CI pipeline

* fixed failing tests

* Modified the analysis_options.yaml

* Fixed warning

* Ran flutter format command

Co-authored-by: Qun Cheng <quncheng@google.com>
Co-authored-by: hangyu <108393416+hangyujin@users.noreply.github.com>

tool/flutter_ci_script_master.sh

@@ -25,6 +25,7 @@ declare -ar PROJECT_NAMES=(
     # "experimental/web_dashboard"
     # Needs a reformat to work on master
     # "experimental/linting_tool"
+    "experimental/material_3_demo"
     "flutter_maps_firestore"
     # TODO(domesticmouse): re-enable when stable increments
     # "form_app"