Allow drag/drop of display blocks

After dropping, apply the new topology to the DisplayManager. We assume
the new topology is immediately written and read it back.

We don't yet respond to updates of the topology from other apps or
components; this will come in a follow-up patch soon.

Flag: com.android.settings.flags.display_topology_pane_in_display_list
Bug: b/352650922
Test: drag a display when there is only one in the topology
Test: drag a display when there are two in the topology
Test: close and re-open settings to verify a topology is persisted
Test: atest DisplayTopologyPreferenceTest.kt
Change-Id: I26aa7325570c5fd3e8b5fb60cb6e1196f8657b80