[11u] RFR: 8231586: enlarge encoding space for OopMapValue offsets

[Lindenmaier, Goetz]

Hi,

I would like to downport this for parity with 11.0.9-oracle.

I had to resolve oopMap.cpp:326.
The code indented within the new if (omv.type() == OopMapValue::derived_oop_value) differs slightly.

http://cr.openjdk.java.net/~goetz/wr20/8231586-OopMapValues-jdk11/webrev/
https://bugs.openjdk.java.net/browse/JDK-8231586
https://hg.openjdk.java.net/jdk/jdk/rev/f9cc0141574c

Please review.

Best regards,
 Goetz.