gtk/window: remove GtkWindowGeometryInfo from public header file

GtkWindowGeometryInfo is only used by static methods in gtkwindow.c
so it doesn't need to be in the public header file.

docs/reference/gtk/gtk4-sections.txt

@@ -4668,7 +4668,6 @@ GTK_WINDOW_GET_CLASS
 <SUBSECTION Private>
 GtkWindowPrivate
 gtk_window_get_type
-GtkWindowGeometryInfo
 gtk_window_remove_embedded_xid
 gtk_window_add_embedded_xid
 GtkWindowKeysForeachFunc

gtk/gtkwindow.c

@@ -158,6 +158,8 @@
  * instead.
  */
 
+typedef struct _GtkWindowGeometryInfo GtkWindowGeometryInfo;
+
 typedef struct
 {
   GtkWidget             *child;

gtk/gtkwindow.h

@@ -44,7 +44,6 @@ G_BEGIN_DECLS
 #define GTK_WINDOW_GET_CLASS(obj)       (G_TYPE_INSTANCE_GET_CLASS ((obj), GTK_TYPE_WINDOW, GtkWindowClass))
 
 typedef struct _GtkWindowClass        GtkWindowClass;
-typedef struct _GtkWindowGeometryInfo GtkWindowGeometryInfo;
 typedef struct _GtkWindowGroup        GtkWindowGroup;
 typedef struct _GtkWindowGroupClass   GtkWindowGroupClass;
 typedef struct _GtkWindowGroupPrivate GtkWindowGroupPrivate;