Create a desktop shell command handler.

Introduce a shell command to move a task into desktop mode using its
task id. Currently
there are no animations as the transition is handled by the default
handler.

Test: adb shell dumpsys activity service SystemUIService WMShell
desktopmode moveToDesktop <taskId> moves task to desktop
Bug: 314313570

Change-Id: I68486290e7dc2be6f8d7099532d3c67f9c96ee9f