Called when the user taps on this selectable text.
The selectable text builds a GestureDetector to handle input events like tap, to trigger focus requests, to move the caret, adjust the selection, etc. Handling some of those events by wrapping the selectable text with a competing GestureDetector is problematic.
To unconditionally handle taps, without interfering with the selectable text's internal gesture detector, provide this callback.
To be notified when the text field gains or loses the focus, provide a focusNode and add a listener to that.
To listen to arbitrary pointer events without competing with the selectable text's internal gesture detector, use a Listener.
final GestureTapCallback onTap