scanner: Enable LRM and RLM marks for BiDi text
Enable displaying bidirectional text in XKB files using:
- U+200E LEFT-TO-RIGHT MARK
- U+200F RIGHT-TO-LEFT MARK
We now parse these marks as white space. As such, they are dropped;
note that a later serialization may not display correctly without
the marks, although it will parse.
References:
- https://www.w3.org/International/articles/inline-bidi-markup/uba-basics
- https://www.w3.org/International/questions/qa-bidi-unicode-controls
- https://www.unicode.org/reports/tr31/#Whitespace
- https://www.unicode.org/reports/tr55/