Exit split-screen if one of the splits is empty

Unusual use cases result in the split being empty.The case happens if
the intent is the same app but not support multi-instance, we should
exit split and expand that app as full screen.

Moreover, apply the same evicts logic from startShortCut to startTask
on this CL.

Bug: 235193477
Test: Launch Google calendar and drag the app to split screen
Change-Id: I1081aaa8303a551f140668c953cd2fd7c4dd3c54