The width of the area within which a horizontal swipe will open the drawer.
By default, the value used is 20.0 added to the padding edge of
MediaQuery.paddingOf(context) that corresponds to alignment.
This ensures that the drag area for notched devices is not obscured. For
example, if alignment is set to DrawerAlignment.start and
TextDirection.of(context) is set to TextDirection.ltr,
20.0 will be added to
final double? edgeDragWidth;