RFR: JDK-8273902: Memory leak in OopStorage due to bug in OopHandle::release()

[Volker Simonis]

Currently, `OopHandle::release()` is implemented as follows:

inline void OopHandle::release(OopStorage* storage) {
  if (peek() != NULL) {
    // Clear the OopHandle first
    NativeAccess<>::oop_store(_obj, (oop)NULL);
    storage->release(_obj);
  }
}

However, peek() returns NULL not only if the oop* `_obj` is NULL, but also when `_obj` points to a zero oop. In the latter case, the oop* `_obj` will not be released from the corresponding OopStorage and the slot it occupies will remain alive forever.

This behavior can be easily triggered with the `LeakTestMinimal.java` test which is attached to the [JBS issue](https://bugs.openjdk.java.net/browse/JDK-8273902)(thanks to Oli Gillespie from the Amazon Profiler team for detecting the issue and providing a reproducer).

This fix should probably also be downported to jdk17 as quickly as possible.

-------------

Commit messages:
 - JDK-8273902: Memory leak in OopStorage due to bug in OopHandle::release()

Changes: https://git.openjdk.java.net/jdk/pull/5549/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5549&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273902
  Stats: 4 lines in 2 files changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5549.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5549/head:pull/5549

PR: https://git.openjdk.java.net/jdk/pull/5549