swift234

Lexer: Lex escaped identifier tokens.

Lex a backtick-enclosed `[:identifier_start:][:identifier_cont:]+` as an identifier, even if it's a Swift keyword. For now, require that the escaped name still be a valid identifier, keyword collisions notwithstanding. (We could in theory allow an arbitrary string, but we'd have to invent a mangling for non-identifier characters and do other tooling which doesn't seem productive.)

Swift SVN r14671