cogl: Move has_feature to Context namespace

That is where it belongs anyways..

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3895>

src/tests/cogl/conform/test-map-buffer-range.c

@@ -34,7 +34,7 @@ test_map_buffer_range (void)
   CoglAttribute *tex_coord_attribute;
   CoglPrimitive *primitive;
 
-  if (!cogl_has_feature (test_ctx, COGL_FEATURE_ID_MAP_BUFFER_FOR_WRITE))
+  if (!cogl_context_has_feature (test_ctx, COGL_FEATURE_ID_MAP_BUFFER_FOR_WRITE))
     {
       g_test_skip ("Missing map buffer for write capability");
       return;