swift234

[CodeCompletion] Fix completion in string literal interpolation at top-level

Mostly this was just returning the ParserStatus bits that we got from
parseExprList from parseExprStringLiteral. The rest was just cleaning up
places that didn't handle EOF very well, which is important here because
the code completion token is buried in the string literal, so the
primary lexer will walk past it.

rdar://problem/17101944