This adds a simple example to CustomMultiChildLayout that lays out colored containers in a cascade.

This reverts commit e78f135f.

* Modularize ReorderableListView auto scrolling logic

* comment

* fix test

* addressing comment

* Bump video_player in flutter gallery

* Update packages

* Update dependencies

* Bump device_info

* Update dev/devicelab/bin/tasks/build_ios_framework_module_test.dart
Co-authored-by: Jenn Magder <magder@google.com>

* Update dev/devicelab/bin/tasks/module_custom_host_app_name_test.dart
Co-authored-by: Jenn Magder <magder@google.com>

* Update dev/devicelab/bin/tasks/module_test.dart
Co-authored-by: Jenn Magder <magder@google.com>

* Remove deprecated device_info from ios-frameworks test
Co-authored-by: Jenn Magder <magder@google.com>

When desktop support is not present in an existing project, certain
flutter tool commands raise an error that direct the user to
documentation on how to add desktop support to an existing Flutter
project. In a recent revamp of the webside, the URL was very slightly
changed (flutter.dev -> docs.flutter.dev).

This updates the error message to output the new URL.

Issue: https://github.com/flutter/flutter/issues/94398