Update unique ID mappings in DisplayTopologyCoordinator

When onDisplayChanged is received and
- the new unique ID isn't null
- the new unique ID is different from the old one
- the display is present in the topology (we already have a mapping for the display)
then update the mapping and restore the topology from the XML file so that the positions by unique ID are preserved.

Bug: 438419983
Test: DisplayTopologyCoordinatorTest
Flag: EXEMPT bugfix
Change-Id: Iece261f7539f3a114b5e707eda92fcfe7d261c16