Instead of special-casing tokens starting with `r`, lex them as normal
identifiers, and add a special case to `#` handling to detect if the
previous token was an `r` identifier.
This roughly doubles the time to lex a raw identifier, because we do two
hash table insertions rather than one, and probably slightly slows down
lexing string literals starting with `#`, but should remove the 2%
overhead to identifier lexing from the previous approach.
Richard Smith
45c071f2af