Handle onActivityReparentToTask for activity in other process

1. Refactor onStartActivity so that we can reuse the same logic for
   onActivityReparentToTask. Also cleanup the logic there.
2. Besides the launching activity, check if the launched activity can be
   split with the top activities.

Bug: 225371112
Test: atest WMJetpackUnitTests:SplitControllerTest
Test: atest WMJetpackUnitTests:TaskContainerTest
Change-Id: I840766e4efaa4bdb9ec89cdca8b3c2c0bbe8cf8c