Add helper functions to the lexer to tokenize strings that have different classifications in ES2 and ES3.

Bug 19331817

Change-Id: I4e1c190e23aa63b03ef8f57930102d01e496f107
Reviewed-on: https://swiftshader-review.googlesource.com/2311Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>