RFR: 8168049: Fix Performance of Lexer.isJSWhitespace

[Hannes Wallnöfer]

Please review:

Bug: https://bugs.openjdk.java.net/browse/JDK-8168049
Webrev: http://cr.openjdk.java.net/~hannesw/8168049/webrev/

This improves parse time by 5 - 10% in most scripts I’ve looked at.

Thanks,
Hannes