Fix wallpaper transition cts test failures

Adjust wallpaper windows if an opening app has a window that can be a
wallpaper target so that the right transition animation can be played.
We previously relied on the chance that a previous layout pass might
have set the target wallpaper correctly.

Bug: 31626368
Test: run-test android.server.cts.ActivityManagerTransitionSelectionTests
Change-Id: Idf5e516f4464944b7a31a55d206f05ca3d4ef407