The `\p{name}` and `\P{name}` character class syntaxes now accept the names
Any, ASCII, Assigned, Cn, and LC, as well as Unicode category aliases like `\p{Letter}` for `\pL`.
Following [Unicode TR18](https://unicode.org/reports/tr18/), they also now use
case-insensitive name lookups, ignoring spaces, underscores, and hyphens.
