attributes: avoid g_strdup in cogl_attribute_new

Calling g_strdup for attribute names was starting to show up in profiles
due to calling malloc for new string storage so frequently. This avoids
calling g_strdup and calls g_intern_string() instead. For the really
common case names we even avoid the cost of g_intern_string since we
can trivially relate our internal name_id to a static string.

Reviewed-by: Neil Roberts <neil@linux.intel.com>

cogl/cogl-attribute-private.h

@@ -45,7 +45,7 @@ struct _CoglAttribute
   CoglObject _parent;
 
   CoglAttributeBuffer *attribute_buffer;
-  char *name;
+  const char *name;
   CoglAttributeNameID name_id;
   gsize stride;
   gsize offset;