compositor: Move edge resistance data to MetaWindowDrag

At least indirectly, this is set as object qdata while the
window drag is ongoing, and reset/reconstructed if needed.

Consequently, this edge data does not need to be stored in
the MetaDisplay struct anymore.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2683>

src/core/display-private.h

@@ -44,8 +44,6 @@
 typedef struct _MetaBell       MetaBell;
 typedef struct _MetaStack      MetaStack;
 
-typedef struct MetaEdgeResistanceData MetaEdgeResistanceData;
-
 typedef enum
 {
   META_LIST_DEFAULT                   = 0,      /* normal windows */
@@ -143,8 +141,6 @@ struct _MetaDisplay
   guint       autoraise_timeout_id;
   MetaWindow* autoraise_window;
 
-  MetaEdgeResistanceData *grab_edge_resistance_data;
-
   MetaKeyBindingManager key_binding_manager;
 
   /* Opening the display */