RFR: 8306687: Relax memory ordering constraints on metaspace atomic counters

[Zhengyu Gu]

Metaspace atomic counter (`SizeAtomicCounter`) is used to track used `class` and `nonclass` metaspace sizes, they are pure counters and only need atomic guarantee.

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Commit messages:
 - v0

Changes: https://git.openjdk.org/jdk/pull/13618/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13618&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306687
  Stats: 5 lines in 1 file changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/13618.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13618/head:pull/13618

PR: https://git.openjdk.org/jdk/pull/13618