Add gdk_surface_get_parent back

The api is the same, the parent is different.
This now returns the parent of popup surfaces.

docs/reference/gdk/gdk4-sections.txt

@@ -181,6 +181,7 @@ GdkSurfaceState
 gdk_surface_new_toplevel
 gdk_surface_new_temp
 gdk_surface_new_popup
+gdk_surface_get_parent
 gdk_surface_destroy
 gdk_surface_get_surface_type
 gdk_surface_get_display

gdk/gdksurface.c

@@ -800,6 +800,26 @@ gdk_surface_new_popup (GdkDisplay *display,
   return surface;
 }
 
+/**
+ * gdk_surface_get_parent:
+ * @surface: a #GtkSurface
+ *
+ * Returns the parent surface of a surface, or
+ * %NULL if the surface does not have a parent.
+ *
+ * Only popup surfaces have parents.
+ *
+ * Returns: (transfer none) (nullable): the parent of
+ *   @surface, or %NULL
+ */
+GdkSurface *
+gdk_surface_get_parent (GdkSurface *surface)
+{
+  g_return_val_if_fail (GDK_IS_SURFACE (surface), NULL);
+  
+  return surface->parent;
+}
+
 static void
 update_pointer_info_foreach (GdkDisplay           *display,
                              GdkDevice            *device,

gdk/gdksurface.h

@@ -436,6 +436,9 @@ GdkSurfaceType gdk_surface_get_surface_type     (GdkSurface     *surface);
 GDK_AVAILABLE_IN_ALL
 gboolean      gdk_surface_is_destroyed          (GdkSurface     *surface);
 
+GDK_AVAILABLE_IN_ALL
+GdkSurface *  gdk_surface_get_parent            (GdkSurface     *surface);
+
 GDK_AVAILABLE_IN_ALL
 GdkDisplay *  gdk_surface_get_display           (GdkSurface     *surface);
 GDK_AVAILABLE_IN_ALL