In order to prevent converting a jsid to a UTF-8 string, only for the
purpose of putting it in a debug message, we introduce gjs_debug_id() and
its friends gjs_debug_value(), gjs_debug_string(), and
gjs_debug_symbol(). If this seems like overkill just to avoid one UTF-8
conversion, it is; but these functions will be used later in the
structured logging code.