Trigger fontconfig initialization early

Add a pango call to create the fontmap already in gtk_init.
This will let us hide the cost of FcInit() (which on font-heavy
systems can be ~100ms) in a thread, on the pango side.

gtk/gtkmain.c

@@ -623,6 +623,9 @@ do_pre_parse_initialization (void)
       slowdown = g_ascii_strtod (env_string, NULL);
       _gtk_set_slowdown (slowdown);
     }
+
+  /* Trigger fontconfig initialization early */
+  pango_cairo_font_map_get_default ();
 }
 
 static void