Component theme normalization updates

BottomAppBarTheme was refactored to conform to Flutter's conventions for component themes. BottomAppBarThemeData was added to define overrides for the defaults of the component visual properties. Releases of Flutter continue to normalize component themes like these for a more consistent theming experience in the material library.

In ThemeData:

• The type of bottomAppBarTheme property has been changed from BottomAppBarTheme to BottomAppBarThemeData.

The return type of the component theme xTheme.of() methods and Theme.of().xTheme have also changed to xThemeData.

Code before migration:

final BottomAppBarTheme bottomAppBarTheme = Theme.of(context).bottomAppBarTheme;
final BottomAppBarTheme bottomAppBarTheme = BottomAppBarTheme.of(context);

final ThemeData theme = ThemeData(
  bottomAppBarTheme: BottomAppBarTheme(),
);

final ThemeData theme = ThemeData().copyWith(
  bottomAppBarTheme: BottomAppBarTheme(),
);

Code after migration:

final BottomAppBarThemeData bottomAppBarTheme = Theme.of(context).bottomAppBarTheme;
final BottomAppBarThemeData bottomAppBarTheme = BottomAppBarTheme.of(context);

final ThemeData theme = ThemeData(
  bottomAppBarTheme: BottomAppBarThemeData(),
);

final ThemeData theme = ThemeData().copyWith(
  bottomAppBarTheme: BottomAppBarThemeData(),
);

Landed in version: Not yet
Stable release: Not yet

API documentation:

• BottomAppBarTheme

Relevant PRs:

• Normalize ThemeData.bottomAppBarTheme