Theme usage doc for some widgets has an incorrect return type.

Actual Results:

The following error is thrown:
A value of type 'TextButtonThemeData' can't be assigned to a variable of type 'TextButtonTheme'.

Expected Results:

/// TextButtonThemeData theme = TextButtonTheme.of(context);

For reference

I've found the following widget theme docs have this issue problem

• TextButtonTheme
• ElevatedButtonTheme
• OutlinedButtonTheme
• DrawerTheme
• NavigationBarTheme
• NavigationRailTheme