wayland: Move the primary data device manager to its own file

Instead of having everything clumped at MetaWaylandDataManager,
split the primary selection to its own struct. This manager is
handled separately from wl_data_device_manager and other selection
managers, so they would be able to interoperate between them, even.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1193

src/wayland/meta-wayland-types.h

@@ -37,6 +37,7 @@ typedef struct _MetaWaylandTouch MetaWaylandTouch;
 typedef struct _MetaWaylandDragDestFuncs MetaWaylandDragDestFuncs;
 typedef struct _MetaWaylandDataOffer MetaWaylandDataOffer;
 typedef struct _MetaWaylandDataDevice MetaWaylandDataDevice;
+typedef struct _MetaWaylandDataDevicePrimary MetaWaylandDataDevicePrimary;
 
 typedef struct _MetaWaylandTabletManager MetaWaylandTabletManager;
 typedef struct _MetaWaylandTabletSeat MetaWaylandTabletSeat;