RFR: CODETOOLS-7902922: jcstress: Tune up generated code once more

[Aleksey Shipilev]

There are more tune ups in generated code in sight:
 - reduce the use of lambdas
 - reduce the use of collections
 - avoid some unnecessary loops
 - avoid excessive message handling

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Commit messages:
 - Tune up generated code in jcstress infra

Changes: https://git.openjdk.java.net/jcstress/pull/50/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=50&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902922
  Stats: 142 lines in 4 files changed: 41 ins; 40 del; 61 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/50.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/50/head:pull/50

PR: https://git.openjdk.java.net/jcstress/pull/50