[jdk11u-dev] RFR: 8315692: Parallelize gc/stress/TestStressRSetCoarsening.java test

[Soumadipta Roy]

The commit includes backporting a564d436c722f14041231158f21c4ad3a2f6a3a5 from upstream to jdk11u-dev. The hunks were not applied cleanly due to the WhiteBox path being different in JDK11(sun.hotspot.WhiteBox) from JDK17 and JDK21(jdk.test.whitebox.WhiteBox). Below are the results upon running in AL2_x86_64:

* before_release: 1345.83s user 96.37s system 507% cpu 4:44.44 total
* before_debug: 6899.97s user 176.88s system 1452% cpu 8:07.25 total
* after_release: 1362.16s user 85.15s system 901% cpu 2:40.53 total
* after_debug: 8678.08s user 90.59s system 3287% cpu 4:26.70 total

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Commit messages:
 - Backport a564d436c722f14041231158f21c4ad3a2f6a3a5

Changes: https://git.openjdk.org/jdk11u-dev/pull/2293/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2293&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315692
  Stats: 68 lines in 1 file changed: 60 ins; 1 del; 7 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2293.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2293/head:pull/2293

PR: https://git.openjdk.org/jdk11u-dev/pull/2293