Port _g_enum_value_to_nick() to C

vapi/c-api.vapi

@@ -204,6 +204,10 @@ namespace Matrix {
         ANSWER;
     }
 
+    /* Utilities */
+    [CCode (cheader_filename = "utils.h", cname = "_matrix_g_enum_to_string")]
+    public string? _g_enum_value_to_nick(GLib.Type enum_type, int value, bool convert_dashes = true);
+
     /**
      * The major version number of the Matrix.org GLib SDK.
      */