Kostia Sokolovskyi d76e3abf10
Fix memory leaks in DateRangePickerDialog. (#136034)
This PR mainly fixes several memory leaks in the `DateRangePickerDialog`.

### Description
- Fixes https://github.com/flutter/flutter/issues/136033 by:
    1) adding a disposal of several `RestorableValue`;
    2) creating a separate `_DayItem` stateful widget that creates/updates/disposes internal `MaterialStatesController`.
- Marks https://github.com/flutter/flutter/issues/136036.

### Tests
- Updates `test/material/date_picker_theme_test.dart` to use `testWidgetsWithLeakTracking`;
- Updates `test/material/date_range_picker_test.dart` to use `testWidgetsWithLeakTracking`.
2023-10-06 11:26:06 +00:00
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