Flexible 2-app split: Parallax (landscape)

This CL implements the correct parallax effects for apps going offscreen and getting pulled back onscreen in landscape mode.

Portrait mode looks good with this patch (no visual bugs), but there is an additional tweak needed (center-aligning the surface) that is complicated enough to defer to another CL.

Bug: 349828130
Flag: com.android.wm.shell.enable_flexible_two_app_split
Test: Visually correct for all landscape CUJs
Change-Id: Iffa8a8bbe55045b15697f325ff3a1f686dfcc565