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

[Hamlin Li]

Membar in PSPromotionManager::copy_unmarked_to_survivor_space could be relaxed.
( Please also refer to the similar membar relaxed in G1ParScanThreadState::do_copy_to_survivor_space )

Per the specjbb2015 test results, it has about 8% improvement in critical.
https://bugs.openjdk.java.net/secure/attachment/95445/jdk17_default_options.v2.png

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

Commit messages:
 - move copy back
 - Optimize PS by moving copying after forwarding successfully during evac

Changes: https://git.openjdk.java.net/jdk/pull/4751/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4751&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8269870
  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4751.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4751/head:pull/4751

PR: https://git.openjdk.java.net/jdk/pull/4751