[jdk17u-dev] RFR: 8306738: Select num workers for safepoint ParallelCleanupTask [v2]

[Aleksey Shipilev]

> Unclean backport to considerably improve the safepoint cleanup times. The backport is not clean, because the `WorkGang` -> `WorkerThreads` rename is missing. The is also the addition of `Dictionary::does_any_dictionary_needs_resizing` check, because JDK 17 is still have that resize code in JDK 17.
> 
> Additional testing:
>  - [x] Ad-hoc benchmarks
>  - [x] Linux x86_64 fastdebug `tier1 tier2 tier3`
> 
> The experiments (see original PR) show we win big on this:
> ![plot](https://github.com/openjdk/jdk17u-dev/assets/1858943/fd69b925-fa69-4e13-ac8c-e0dd72dd43cd)

Aleksey Shipilev 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.

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Changes:
  - all: https://git.openjdk.org/jdk17u-dev/pull/1379/files
  - new: https://git.openjdk.org/jdk17u-dev/pull/1379/files/beb12598..beb12598

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1379&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1379&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1379.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1379/head:pull/1379

PR: https://git.openjdk.org/jdk17u-dev/pull/1379