[23/N] Desks: Deactivate desk when moving to split-screen

Ensures that when moving a deskop window to split-screen its desk is
deactivated (future launches aren't in freeform).

On the split side, this requires applying the split-select WCT using a
shell transition, so that the transition can be tracked by the
DesksTransitionObserver using the transition token.

Flag: com.android.window.flags.enable_multiple_desktops_backend
Bug: 394268248
Test: enter desktop with 1 window, use the app header to move it to
split, verify the desk is deactivated as a result (new launches are not
in freeform and the repository dump shows the desk as deactivated)

Change-Id: Ied4bb547b7b3c25395d80d31aa1439a24321c890