RFR: 8369571: Parallel: Use ThreadsClaimTokenScope in PSAdjustTask

[Albert Mingkun Yang]

Trivial lifting threads claim token logic into using the existing `ThreadsClaimTokenScope`.

Test: tier1

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Commit messages:
 - pgc-thread-claim-scope

Changes: https://git.openjdk.org/jdk/pull/27746/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27746&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369571
  Stats: 7 lines in 1 file changed: 2 ins; 5 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27746.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27746/head:pull/27746

PR: https://git.openjdk.org/jdk/pull/27746