RFR: CODETOOLS-7902921: jcstress: Pre-warmup affinity support and thread pools

[Aleksey Shipilev]

Profiling for "-m sanity" runs shows that we spend considerable amount of time doing the first-use initialization of AffinitySupport in the worker threads. We can make it better by offloading that first initialization to the worker task that runs during the rest of the infra initialization.

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Commit messages:
 - Pre-warmup

Changes: https://git.openjdk.java.net/jcstress/pull/49/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=49&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902921
  Stats: 50 lines in 1 file changed: 38 ins; 12 del; 0 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/49.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/49/head:pull/49

PR: https://git.openjdk.java.net/jcstress/pull/49