Defines the height of the app bar when it is collapsed.
By default, the collapsed height is toolbarHeight. If bottom widget is specified, then its height from PreferredSizeWidget.preferredSize is added to the height. If primary is true, then the MediaQuery top padding, EdgeInsets.top of MediaQueryData.padding, is added as well.
If pinned and floating are true, with bottom set, the default collapsed height is only the height of PreferredSizeWidget.preferredSize with the MediaQuery top padding.
final double? collapsedHeight;