RFR: 8372565: Convert SATBMarkQueue to use Atomic<T>

[Kim Barrett]

Please review this change to SATBMarkQueue to use Atomic rather than directly
applying AtomicAccess to volatile members.

Testing: mach5 tier1-5

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Commit messages:
 - SATB queue uses Atomic

Changes: https://git.openjdk.org/jdk/pull/28525/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28525&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372565
  Stats: 18 lines in 3 files changed: 2 ins; 1 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/28525.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28525/head:pull/28525

PR: https://git.openjdk.org/jdk/pull/28525