Use transition bounds to determine the split index.

The transition animation is apply based on windowConfiguration#getBounds
instead of app bounds, so shouldn't calculate split index based on app
bounds.
Also set the cutout mode to always, so the test activities won't be
affected by any other cutout.
Also adjust the judgement around rounded corners regions. If the rounded
corner is set to a circle, there will be no testable region. So instead
of ignore those area, get the minimal rectangle from them.

Bug: 317742662
Test: enable waterfall cutout, run ActivityTransitionTests
Change-Id: Ib62ca20dc09c23dc127264d45daf26e1d6850adc