Don't show drag mirrors on displays that are not in the topology.

In projected mode, when dragging PiP across displays, the mirror is
sometimes shown on the default display (the phone) but it's not part of
the topology, so the PiP window can't be dragged over to that display.

Fixes: 422699849
Test: atest PipDisplayTransferHandlerTest
Flag: com.android.window.flags.enable_dragging_pip_across_displays
Change-Id: I9fbcb419f6366d22daa884b0c096b94d9338e535