Limit fixed orientation letterbox to split screen and fullscreen on task level.

Before ag/13575049 moved fixed orientation letterbox to activity level, it was allowed only for tasks in fullscreen or split screen windowing modes. After refactoring, the same condition was checked for activity windowing mode which isn't the same. This causes bugs for apps that use PiP mode so moving back to gating fixed orientation letterbox with task windowing mode check.

Fix: 181767614
Fix: 184078928
Test: atest SizeCompatTests and repro steps in both bugs.
Change-Id: I3004f29aa1ba66f9c46d55ed0fe197210c9d4da8