Restore strong reference to animation runner

- The remote animation factory needs to be strongly referenced since
  the only other reference is a weakly held one from
  LauncherAnimationRunner, and if a gc happens in between starting
  the animation and the onAnimationStart() callback, then the
  animation will not play.

Fixes: 284106887
Test: Force a gc after creating a remote app launch animation and ensure
      that the runner still exists when the animation starts
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:6cfe2e6cbe52f5fc9aa0eb94afaeb7679810cc13)
Merged-In: I5f584451b41c666916801b8ea0cb470c7ab9fc51
Change-Id: I5f584451b41c666916801b8ea0cb470c7ab9fc51