Stub impl new multi-desks `IDesktopTaskListener` APIs

This CL chain adds the new multi-desks APIs in `IDesktopTaskListener`
and a stub implementation in
`DesktopVisibilityController.DesktopTaskListenerImpl`.
Follow-up CLs will add the real impls.

Bug: 392978600
Test: m
Flag: EXEMPT new APIs without impl yet.
Change-Id: I360ef179769df16dbcf12a01d19d57a88bc82262