Stringifier attributes vs methods are treated differently

[tabatkins]

In whatwg/url#288 (comment), Anne said:

@tabatkins so the weird thing is that in stringifier attribute USVString href; href is seen as an attribute but in stringifier USVString toJSON () toJSON() is seen as a stringifier instead of a method. Why is that?

[annevk]

It would be nice to make some progress here although I suppose one solution might be to remove toJSON() for now.