locatePointer: Add implementation in gnome-shell
The "locate pointer" functionality was implemented in gnome settings daemon using X11 protocols and would fail when run under Wayland.
With Wayland, there is no global coordinate space exposed to the clients so this functionality cannot be implemented as a separate program.
Instead, add the "locate pointer" functionality in gnome-shell so that it works in both X11 and Wayland.
Edited by Olivier Fourdan