Couple fixes for M11nGestureHandler

1. Added missing defensive copy for a MotionEvent that is posted
asynchronously with delay, and thus might get recycled
2. Fixed transitioning to viewport dragging on 3tap/shortcut+swipe

Test: manually ensure the fix is working
Bug: 73359125
Change-Id: Iae8cd3a83512ee363abe9f0b5702287d7616c092