Check that activity is not in PIP mode already

This change verifies that the requested activity to PIP
is not already in PIP mode before scheduling a transaction
with an EnterPipRequestedItem.

Bug: 156365025
Test: atest WmTests:ActivityTaskManagerServiceTests
Change-Id: I37019368b00440bdd24cb3ee5f4bfaf667464f8a
2 files changed