Enable forced focus for resumed split screen activities

This is needed because some game engines wait until they get focus before drawing the content of the app so they are blacked out when they are resumed and do not have focus yet.

Bug: 203398248
Test: atest FrameworksCoreTests:ViewRootImplTest#whenDispatchFakeFocus_noFocusAfterwards
Change-Id: I5675b32fbb9f60a7373fadbce379d571168436e7