Some fixes for transition animation selection

- Request wallpaper adjust after we clear mDestroying or
  mAnimatingExit flags, as these could affect wallpaper
  target selection result.

- Adjust wallpaper before we check lower/upper target. As
  there could be pending operations that requested a wall-
  paper update. Lower/upper target is needed to correctly
  decide if the opening or closing apps had wallpaper.

- Make sure lower/upper targets are set even when current
  target is clientHidden, in which case we should set
  wallpaper target to old target but the lower/upper
  still needs to be set up.

bug: 30255354
Change-Id: Ie2c94439142cbb91660c5aa4164cc660831486d5