Fix enter/exit horizontal ActivityEmbedding split with Shell transition

1. For animation spec, before, we only consider animation to/from
   left/right. Now, we also check top/bottom.
2. For animation adapter, before, we always use the window end bounds,
   which may be empty when closing a window that is also resizing during
   the transition. Now, for closing window, we use the start bounds
   instead.

Bug: 241043533
Test: Verify with launching activity into horizontal split.
Test: Verify with switching between split and stack.
Change-Id: I4fddcb2327d05e90b0c12605490fa7d7aa987fa0