Account for stopping activities when determining whether to restart

- We were seeing a flakey issue with gesture nav, when swiping
  immediately after launching an app, the system would stop
  launcher, but shortly after, we would start the recents animation
  for the next gesture. The recents animation calls:

  [RWC->DC->AS].ensureActivitiesVisible()
  -> EnsureActivitiesVisibleHelper.setActivityVisibilityState()
  -> AR.makeActiveIfNeeded()
  -> AR.shouldStartActivity()

  and the visible is requested, but we are currently still stopping
  because the client hasn't called back. This results in the
  animation continuing, but the system silently not scheduling
  launcher to be started, which prevents a draw-callback to finish
  on the client side, which then prevents us from finishing the
  recents animation (we are waiting for the draw to update the task
  view with the snapshot).

Bug: 151788100
Test: Manual, it's hard to repro but you just have to swipe up after
      launching apps really quickly to get stuck in a state where you
      can't swipe up at all

Change-Id: I32628f1e532764fc1ef962c6d4602214ca7c36c4