Missing FloatingActionButtonTheme

[bleroux]

Use case

Customize FloatingActionButton visual properties in a sub-tree through an InheritedTheme widget.
Similarly to what is possible for most widgets.

Proposal

Add FloatingActionButtonTheme.
This missing theme class was mentioned in flutter.dev/go/material-theme-system-updates:
"FloatingActionButtonThemeData is conformant but there’s no FloatingActionButtonTheme class. "

Sample usage:

  Widget build(BuildContext context) {
    return FloatingActionButtonTheme(
      data: const FloatingActionButtonThemeData(iconSize: 56),
      child: Scaffold(
        floatingActionButton: FloatingActionButton(child: const Icon(Icons.adb), onPressed: () {}),
      ),
    );
  }