Set a relative layer instead of reparenting launch animations.

Reparenting makes the animating window inherit the new parent's
transforms, which creates all sorts of issues. By simply moving
the layer to the front we can avoid all these problems.

Note that there remains one issue with this new approach: AppZoomOut
does not exclude the launching windows, which are mistakenly
cropped. We're tracking this in b/407021260.

Bug: 406484328
Bug: 404508609
Bug: 406252550
Flag: com.android.systemui.move_transition_animation_layer
Test: atest ActivityTransitionAnimator + manually confirmed that the impacted animations are fixed
Change-Id: I96552964fe64b9ebc7210c4cef38b4addddfb190