Desks: Deactivate desk of correct user on Home launches

Home can be launched as a result of a user switch and the transition can
be handled by Shell before knows about the user change. Use the
TaskInfo#mUserId to obtain the correct DesktopRepository, and thus
deactivate the active desk of the user that will actually have Home
launched over the desk.

Flag: com.android.window.flags.enable_multiple_desktops_backend
Bug: 404591902
Test: switch to user that had Home visible from a user with a desk
visible, check the desk isn't deactivated.

Change-Id: If013ce4add2a9af6d8a0e175ce3e4cfad42276a3