RFR: 8365922: Parallel: Group uses of GCTimeRatio to a single location [v2]

[Albert Mingkun Yang]

> Unify all accesses of `GCTimeRatio` to a single place so that Parallel gets a coherence view of its value within the pause, if the global variable's value is ever changed.
> 
> 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 three additional commits since the last revision:

 - review
 - Merge branch 'master' into pgc-gc-time-ratio-prepare-management
 - pgc-gc-time-ratio-prepare-management

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26881/files
  - new: https://git.openjdk.org/jdk/pull/26881/files/fd6b6e94..b26072e2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26881&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26881&range=00-01

  Stats: 7855 lines in 241 files changed: 5021 ins; 1815 del; 1019 mod
  Patch: https://git.openjdk.org/jdk/pull/26881.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26881/head:pull/26881

PR: https://git.openjdk.org/jdk/pull/26881