RFR[L]: 8237767 Field layout computation overhaul

[Frederic Parain]

Greetings,

Please review this change proposing a new code to compute field layouts.

CR: https://bugs.openjdk.java.net/browse/JDK-8237767
webrev: http://cr.openjdk.java.net/~fparain/jdk_layout/webrev.04/

The CR includes a detailed description of the motivation and the implementation.

The current version keeps the old code accessible (with a VM flag) in case the
small changes in computed layouts cause troubles to some applications or tools.
The goal is to get rid of this old code, preferably as soon as possible.

Testing tier1-8.

Thank you,

Fred