Fix issue with quickswitch happening after recents animation starting

- When the animation starts, prevent quickswitch until the next gesture
  starts
- Refactor recents animation started signal into the gesture helper to
  simplify the code in the nav bar view

Bug: 67957962
Bug: 70180755
Bug: 73080940
Test: Quick scrub on nav bar

Change-Id: I718d3e64c14569e5df2e6a0ffc1aecdb0125f54f
Signed-off-by: Winson Chung <winsonc@google.com>