RFR: 8269870: PS: Membar in PSPromotionManager::copy_unmarked_to_survivor_space could be relaxed

[Albert Mingkun Yang]

The acquire-release mem-barrier was probably used/required before but not any more. Inspiration taken from `G1ParScanThreadState::do_oop_evac`.

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Commit messages:
 - pgc-relax-forward

Changes: https://git.openjdk.org/jdk/pull/19764/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19764&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8269870
  Stats: 6 lines in 1 file changed: 0 ins; 5 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19764.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19764/head:pull/19764

PR: https://git.openjdk.org/jdk/pull/19764