RFR: 8334445: Parallel: Decouple maximum compaction from SoftReference clearing [v2]

[Albert Mingkun Yang]

> Simple refactoring to not assume maximum-compaction from soft-ref-clearing.

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-max-compact
 - pgc-max-compact

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19763/files
  - new: https://git.openjdk.org/jdk/pull/19763/files/b341d35f..ce280652

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19763&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19763&range=00-01

  Stats: 26711 lines in 471 files changed: 17674 ins; 6579 del; 2458 mod
  Patch: https://git.openjdk.org/jdk/pull/19763.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19763/head:pull/19763

PR: https://git.openjdk.org/jdk/pull/19763