RFR: 8167289 : Backport ES6 updates from Graal.js

[Hannes Wallnöfer]

Please review:

Bug: https://bugs.openjdk.java.net/browse/JDK-8167289
Webrev: http://cr.openjdk.java.net/~hannesw/8167289/webrev.00/

These is mostly refactoring Andreas did in the Graal.js parser. It also contains minor ES6 parsing fixes. Tests for these will be included together with other additional ES6 tests I’m working on, but I wanted to do a separate commit for the backport, so this issue is labeled noreg-cleanup.

Thanks,
Hannes