RFR: 8328792: Parallel: Refactor PSParallelCompact::summary_phase [v4]

[Albert Mingkun Yang]

> The diff is not easy to follow; it's better to read the new code directly. `summary_phase` contains the gist of collecting live-size from each space, calculating dense-prefix and summarizing old-space using dense-prefix.
> 
> (There is slight improvement to the "Summary Phase", but it takes only ~0.01ms for either case.)

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 one additional commit since the last revision:

  pgc-compute-dense-prefix

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18451/files
  - new: https://git.openjdk.org/jdk/pull/18451/files/69d7d542..3903dc43

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18451&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18451&range=02-03

  Stats: 5253 lines in 123 files changed: 1670 ins; 2584 del; 999 mod
  Patch: https://git.openjdk.org/jdk/pull/18451.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18451/head:pull/18451

PR: https://git.openjdk.org/jdk/pull/18451