Deprecate clutter_[sg]et_font_flags()

We already have two mechanisms for controlling the font rendering
quality on a per-application basis:

  • ClutterSettings properties
  • clutter_backend_set_font_options()

The font flags were always a stop-gap solution, and one that tried to
simplify a fairly complex issue beyond the point of actually being
useful.

https://bugzilla.gnome.org/show_bug.cgi?id=660786

clutter/clutter-types.h

@@ -429,6 +429,8 @@ typedef enum {
  * clutter_set_font_flags().
  *
  * Since: 1.0
+ *
+ * Deprecated: 1.10: Use the #ClutterBackend and #cairo_font_options_t instead
  */
 typedef enum
 {