Allow gestures after end of line

Previous behavior was that point-based handwriting gestures (insert,
remove space, join/split) were supported up to the end of text on each
line (plus 16dp margin).

New behavior is to allow gestures at points after the end of the text up
to the layout width (plus 16dp margin).

Bug: 266253425
Test: atest android.widget.cts.TextViewHandwritingGestureTest
Change-Id: Ib5ac6117788a88c61778326fa5125d4c8199c868