[flexiglass] Fixes extraneous haptic feedback in pattern bouncer.

There's a bug where we vibrate when we first open the bouncer UI in the
pattern configuration and when we stop dragging. This CL fixes that.

Bug: 281871687
Test: manually verified that, after the fix, we only get haptic feedback
when selecting a new dot and not when we first bring up the UI nor when
we stop dragging.

Change-Id: I808698e74a3d9300c11b7422fc70dfdfc5fea80b