Desks: Do not reuse other display's desks

When reusing root tasks from other users, also check that the root task
belongs to the intended display.

Flag: com.android.window.flags.enable_multiple_desktops_backend
Bug: 399394443
Test: atest RootTaskDesksOrganizerTest
Change-Id: I97d63d7837fe490632c61e8229625a651687eaeb