Disallow presentation on unfocused host task

Previoulsy, we only checked the globally focused task if it could
be the host task of a presentation. However, some apps try to
launch a presentation even when it's not focused (as long as they
are resumed they assume that they are on top).

Instead, with this change, the top "visible" task from the same
app is considered to be the host task.

Flag: com.android.window.flags.enable_presentation_disallowed_on_unfocused_host_task
Bug: 435586251
Test: PresentationControllerTests#testPresentationCannotCoverUnfocusedHostTask
Change-Id: Id6bcbf2a31104317522c3790bf196c50bccd982a