Description

• Adds ScrollController creation dispatching for memory leak tracking.

Related Issues

• Fixes: Memory Leak: _ModalScopeState doesn't dispose primaryScrollController #133748;
• Marks memory leak: Memory Leak: _TabBarViewState creates a new PageController each time didChangeDependencies is called #133755.

Tests

• Updates scroll_controller_test.dart to test object creation dispatch;
• Updates app_bar_test.dart to fix non-disposal of ScrollControllers in tests;
• Updates refresh_indicator_test.dart to fix non-disposal of ScrollControllers in tests;
• Updates scrollbar_theme_test.dart to fix non-disposal of ScrollControllers in tests;
• Updates scrollbar_test.dart to fix non-disposal of ScrollControllers in tests and mark memory leaks;
• Updates tabbed_scrollview_warp_test.dart to mark memory leaks;
• Updates page_selector_test.dart to mark memory leaks.

There is no test for routes.dart, because _ModalScope is used in MaterialPageRoute which is used in MaterialApp. Thus any testWidgetsWithLeakTracking which pumps MaterialApp test ScrollController disposal under the hood.

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• All existing and new tests are passing.