Fix regression in assist data fetching and canceling

- We need to be requesting the assist data before showing the target
  activity (since it depends on the currently visible activities)
- Also should be canceling the request when the animation is canceled, this
  can happen when tapping the home button quickly when the animation kicks
  off an assist data request and before the request completes, we've
  canceled the request for the transition home.

Bug: 73312877
Test: Cancel the recents animation, ensure the associated data request
      handler is not called back

Change-Id: Idb3aa266e6b4e14aa12c97fc868c39ab08f35591