RFR: 8321806: Shenandoah: each mutator must see FullGC or GC overhead limit is exceeded before throwing OOM [v4]

[Kelvin Nilsen]

> Require each thread to observe unproductive Full GC before it throws OOM exception.

Kelvin Nilsen has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 12 commits:

 - Merge branch 'master' of https://git.openjdk.org/jdk into fix-fullgc-race
 - Restrict GCTimeLimit if ParallelGCThreads > active_processors
 - Improve message for failure of TestThreadCounts
 - Merge branch 'master' of https://git.openjdk.org/jdk into fix-fullgc-race
 - Fix whitespace
 - Fix up defaults and add quick-OOM following unproductive GCs
 - Fix allocation retry loop and update comments
 - Merge branch 'master' of https://git.openjdk.org/jdk into fix-fullgc-race
 - Implement gc_overhead_exceeds_limit support
 - Fix several bugs for GCU limit exceeded implementation
 - ... and 2 more: https://git.openjdk.org/jdk/compare/fb822e49...b46512ad

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Changes: https://git.openjdk.org/jdk/pull/16985/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16985&range=03
  Stats: 469 lines in 12 files changed: 431 ins; 1 del; 37 mod
  Patch: https://git.openjdk.org/jdk/pull/16985.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16985/head:pull/16985

PR: https://git.openjdk.org/jdk/pull/16985