[css-ruby] Remove issue about auto-hide text comparison and clarify interaction with text-transform: using DOM text is easier since all implementations maintain a copy of the DOM text, but not all maintain one of post-collapsed text. (Best for authors would be after white-space collapsing and before text-transform, but probably few people will run into a case where it matters.) It must be prior to text-transform because 'text-transform: large-kana' is a relevant use case for ruby.