Add a no-op animation for non-changing apps during change transition

Without this, other closing apps during a change transition would
immediately turn invisible because they had no animation. By adding
a no-op, it basically keeps everything visible and stationary until
the transition finishes.

Bug: 113252739
Test: Manual, wallpaper remains visible while maximizing freeform app
Change-Id: I968280ae2915eb571b33a73a1f182228bc8fec74