swift234

Lex $notAllDigits as an identifier and diagnose it in the lexer
outside of debugger-support mode.  Rip out the existing special-case
code when parsing expr-identifier.

This means that the Lexer needs a LangOptions.  Doug and I
talked about just adding that as a field of SourceMgr, but
decided that it was worth it to preserve the possibility of
parsing different dialects in different source files.

By design, the lexer doesn't tokenize fundamentally differently
in different language modes; it might decide something is invalid,
or it might (eventually) use a different token kind for the
same consumed text, but we don't want it deciding to consume more or
less of the stream per token.

Note that SIL mode does make that kind of difference, and that
arguably means that various APIs for tokenizing need to take a
"is SIL mode" flag, but we're getting away with it because we
just don't really care about fidelity of SIL source files.

rdar://14899000

Swift SVN r13896