RFR: 8299125: UnifiedOopRef in JFR leakprofiler should treat thread local oops correctly [v4]

[Axel Boldt-Christmas]

> 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.

Axel Boldt-Christmas has updated the pull request incrementally with one additional commit since the last revision:

  stefank suggestion

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11741/files
  - new: https://git.openjdk.org/jdk/pull/11741/files/b82e8997..9d9637a2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11741&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11741&range=02-03

  Stats: 12 lines in 1 file changed: 5 ins; 0 del; 7 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