RFR (M) 8186088: ConstantPoolCache::_resolved_references is not a JNIHandle

[coleen.phillimore at oracle.com]

Summary: Make an OopHandle type to replace jobject to encapsulate these 
oop pointers in metadata and module entry.

This replaces places where there's a jobject that doesn't point into the 
JNIHandles, notably things allocated in ClassLoaderData::_handles.

There were platform specific changes that I tried to carefully make - 
can someone test them for s390, aarch64 and ppc?

Tested with tier1 testing, JPRT (all oracle platforms), nsk.jvmti, 
monitoring, parallel class loading and g1class unloading tests.

open webrev at http://cr.openjdk.java.net/~coleenp/8186088.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8186088

Thanks,
Coleen