RFR: 8374328: Convert simple AtomicAccess uses in gc/shared to use Atomic<T> [v3]

[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`.
> 
> The changes are grouped into a series of commits, as a potential aid to reviewers.
> 
> Testing: mach5 tier1-5

Kim Barrett 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 eight additional commits since the last revision:

 - Merge branch 'master' into simple-gc-shared-atomic
 - update copyrights
 - pretouch
 - WorkerThread control
 - SuspendibleThreadSet control
 - GCLocker control
 - ConcurrentGCThread termination protocol
 - DeoptimizeNMethodBarriersALot gating counter

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28987/files
  - new: https://git.openjdk.org/jdk/pull/28987/files/ad121490..c07dae40

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28987&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28987&range=01-02

  Stats: 20206 lines in 1812 files changed: 4190 ins; 2467 del; 13549 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