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

[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
 - [ ] 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)

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Depends on: https://git.openjdk.org/jdk17u-dev/pull/1377

Commit messages:
 - Backport 672bade522b4641ffc30b0ac09791e8dcf21e003

Changes: https://git.openjdk.org/jdk17u-dev/pull/1379/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1379&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306738
  Stats: 124 lines in 7 files changed: 112 ins; 4 del; 8 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