RFR: 8374328: Convert simple AtomicAccess uses in gc/shared to use Atomic<T>

[Kim Barrett]

Please review these fairly simple changes to code in gc/shared to use
`Atomic<T>` instead of directly using `AtomicAccess`.

This change doesn't eliminate all remaining direct uses of `AtomicAccess` in
that directory; there are still a few uses that seem less simple, and maybe
some that should stay with direct `AtomicAccess`.

Testing: mach5 tier1-5

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Commit messages:
 - pretouch
 - WorkerThread control
 - SuspendibleThreadSet control
 - GCLocker control
 - ConcurrentGCThread termination protocol
 - DeoptimizeNMethodBarriersALot gating counter

Changes: https://git.openjdk.org/jdk/pull/28987/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28987&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374328
  Stats: 57 lines in 12 files changed: 9 ins; 3 del; 45 mod
  Patch: https://git.openjdk.org/jdk/pull/28987.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28987/head:pull/28987

PR: https://git.openjdk.org/jdk/pull/28987