RFR: 8327387: G1: Refactor region liveness processing after completion of concurrent marking [v2]

[Albert Mingkun Yang]

> The diff is not quite easy to follow. Instead, I'd recommend to read the new code directly, and the entry-point (and the gist) is in `G1OnRegionClosure::do_heap_region`.
> 
> While running BigRamTester, h2, and specjbb2015-fixed, a slight reduction in subphase time (approximately 0.01ms) was observed. However, it's important to note that these subphases are already quite brief in baseline.
> 
> Test: tier1-6

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 three additional commits since the last revision:

 - review
 - Merge branch 'master' into g1-merge-remark
 - g1-merge-remark

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18127/files
  - new: https://git.openjdk.org/jdk/pull/18127/files/a6474cdb..51231eb3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18127&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18127&range=00-01

  Stats: 69095 lines in 617 files changed: 1039 ins; 67002 del; 1054 mod
  Patch: https://git.openjdk.org/jdk/pull/18127.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18127/head:pull/18127

PR: https://git.openjdk.org/jdk/pull/18127