Text methods report a clear error on an empty or missing value

Text handling brought closer to the standard. Calling a text method with nothing to work on, when the value is empty or missing, now reports a clear error the way every other browser does, instead of quietly treating it as the words null or undefined and carrying on with the wrong result. The same clear error is reported for the special symbol values that cannot be turned into text. Every other value keeps working exactly as before. Code that was already correct is unchanged. The JavaScript language aspect moves 98 to 99; the overall platform score stays at 70.