Fix black flash when launching dual split activity

The root cause is that the closing Activity is shrunck because
it also matches the split pair rule with the started activity.

This CL uses the snapshot to show closing transition instead,
and also takes the start bounds into account because the end bounds
of the closing transition may be shrunk.

Test: manual - repro steps in bug with layout direction
      RIGHT_TO_LEFT, TOP_TO_BOTTOM and LOCALE
Bug: 275034335
Change-Id: I63df42f61f03e511f2845899b2576432021ccf49