buildHandle method Null safety
Builds a selection handle of the given
The top left corner of this widget is positioned at the bottom of the selection position.
onTap should be invoked when the handle is tapped, if such
interaction is allowed. As a counterexample, the default selection handle
on iOS cupertinoTextSelectionControls does not call
onTap at all,
since its handles are not meant to be tapped.
Widget buildHandle(BuildContext context, TextSelectionHandleType type, double textLineHeight, [VoidCallback? onTap]);