Run transitions when starting into paused and use starting-windows for split

Starting activities into resumed state would wait until
resumed to execute transitions. However, if a new activity
starts into the primary-split, it actually starts in paused
state. This is valid, but transitions weren't being
executed.

Second, we avoided starting-windows for split-screen before there
were hierarchical animations to avoid clipping issues. Now that
animations are hierarchical, this shouldn't be a problem.

Bug: 155345309
Test: Cold-start an activity into primary-split. Observe an
      immediate starting-window.
Change-Id: I54d80b3faf45981e3b512548d32aada6e08b5241