[css-writing-modes] Support rtl Chinese #2754
Description
Traditionally, CJK text writes and reads vertically, but sometimes it is preferred to write horizontally. Especially when the text is used for some title-line kind things, such as a park name, a shop name, etc.
But traditional horizontal CJK text is different from horizontal-tb, it reads from right to left.
So I suggest adding a new value horizontal-tb-rl to writing-mode.
Note that it doesn't mean that horizontal-tb will only be used for LTR text from now on.
horizontal-tb can still be both LTR and RTL. Those languages which can ONLY be written right to left (such as Arabic, Hebrew) will always be written from right to left no matter whether it's in horizontal-tb or horizontal-tb-rl.