RFR: 8365557: Parallel: Refactor ParallelScavengeHeap::mem_allocate_work [v2]

[Albert Mingkun Yang]

> Extract out multi-thread-safe old-gen allocation API call outside the critical-region to streamline the flow in `mem_allocate_work`.
> 
> Test: tier1-3

Albert Mingkun Yang 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 two additional commits since the last revision:

 - Merge branch 'master' into pgc-mem-allocate-refactor
 - pgc-mem-allocate-refactor

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26779/files
  - new: https://git.openjdk.org/jdk/pull/26779/files/d738b1e4..1160f143

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26779&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26779&range=00-01

  Stats: 32243 lines in 1317 files changed: 21682 ins; 5780 del; 4781 mod
  Patch: https://git.openjdk.org/jdk/pull/26779.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26779/head:pull/26779

PR: https://git.openjdk.org/jdk/pull/26779