gitypelib: Add boxed type

This is needed because `GITypelib` is exposed in the public
libgirepository API, so needs to be introspectable.

This should fix a couple of warnings about `gi_repository_require()` and
related APIs not being introspectable as they return an unintrospectable
type.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Helps: #3155

girepository/gitypelib.c

@@ -41,6 +41,8 @@
  * Since: 2.80
  */
 
+G_DEFINE_BOXED_TYPE (GITypelib, gi_typelib, gi_typelib_ref, gi_typelib_unref)
+
 typedef struct {
   GITypelib *typelib;
   GSList *context_stack;

girepository/gitypelib.h

@@ -36,6 +36,10 @@ G_BEGIN_DECLS
 
 typedef struct _GITypelib GITypelib;
 
+#define GI_TYPE_TYPELIB (gi_typelib_get_type ())
+GI_AVAILABLE_IN_ALL
+GType gi_typelib_get_type (void) G_GNUC_CONST;
+
 GI_AVAILABLE_IN_ALL
 GITypelib *    gi_typelib_new_from_bytes       (GBytes  *bytes,
                                                 GError **error);