Expose current viewport transform of PointerController

This CL adds API to expose the current viewport transform of the
PointerController. This will be used by Choreographer to find the target
display and cursor position in the topology, when cursor moves across
the displays.

Test: presubmit
Bug: 367660694
Flag: com.android.input.flags.connected_displays_cursor

Change-Id: If4fe9fade2bf55f29db377661820ef7a8ca73ba2