Ensure host task has global focus when presenting on internal display

After polishing the code in ag/35225150 just before submission, I
accidentally removed the part that checks global focus.

This change simply readds the part, which was already reviewd in
the previous CL.

Flag: com.android.window.flags.enable_presentation_disallowed_on_unfocused_host_task
Bug: 435586251
Test: PresentationControllerTests
Change-Id: Ie8e0f0f2384f24d3b06e27f73f25f8225dd6d508