RFR: 8299125: UnifiedOopRef in JFR leakprofiler should treat thread local oops correctly

Tue Dec 20 16:38:32 UTC 2022

In a similar vain to [JDK-8299089](https://bugs.openjdk.org/browse/JDK-8299089) there are different semantics for OopStorage and thread local oops. UnifiedOopRef in the jfr leakprofiler must be able to distinguish these and treat them appropriately.

Testing: Running test at the moment. Has been running on the generational branch of ZGC for over three months. Not many tests exercise the leakprofiler. x86_32 has mostly been tested with GHA. 

Note: The accessBackend changes are only there to facilitate comparing OopLoadProxy objects directly with nullptr instead of creating and comparing with an `oop()` / `oop(NULL)`. Can be backed out of this PR and put in a different RFE instead.

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Commit messages:
 - UPSTREAM: UnifiedOopRef changes

Changes: https://git.openjdk.org/jdk/pull/11741/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11741&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299125
  Stats: 100 lines in 4 files changed: 76 ins; 6 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/11741.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11741/head:pull/11741

PR: https://git.openjdk.org/jdk/pull/11741