Add a helper function to the lexer to tokenize strings that can be identifiers in ES2 and are keywords in ES3.

For instance, uint, or the non-square matrix keywords.

TRAC #23218

Signed-off-by: Geoff Lang
Signed-off-by: Nicolas Capens
Author: Jamie Madill

git-svn-id: https://angleproject.googlecode.com/svn/branches/es3proto@2390 736b8ea6-26fd-11df-bfd4-992fa37f6226