RFR: 8374678: ZGC: Convert zForwarding to use Atomic<T> [v2]

[Axel Boldt-Christmas]

> Convert usages of AtomicAccess to Atomic<T> in zForwarding.
> 
> `_ref_count` is unused by the SA. There is currently no implementation of Atomic<T> in SA.
> 
> Testing:
>  * GHA
>  * Tier 1-2 with ZGC linux x64 and linux aarch64
>  * Stress tests with ZGC linux x64 and linux aarch64

Axel Boldt-Christmas has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Use compare_set
 - Merge remote-tracking branch 'upstream_jdk/master' into JDK-8374678
 - ZGC: Convert zForwarding to use Atomic<T>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29220/files
  - new: https://git.openjdk.org/jdk/pull/29220/files/e981013a..e10b6142

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29220&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29220&range=00-01

  Stats: 35662 lines in 505 files changed: 22535 ins; 8490 del; 4637 mod
  Patch: https://git.openjdk.org/jdk/pull/29220.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29220/head:pull/29220

PR: https://git.openjdk.org/jdk/pull/29220