RFR: 8369997: Tests that use custom scheduler should use jdk.test.lib.thread.VThreadScheduler

[Brian Burkhalter]

Straightforward update of some tests which use core reflection to set the `Thread.Builder` scheduler.

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Commit messages:
 - 8369997: Tests that use custom scheduler should use jdk.test.lib.thread.VThreadScheduler

Changes: https://git.openjdk.org/jdk/pull/27855/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27855&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369997
  Stats: 69 lines in 3 files changed: 9 ins; 53 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/27855.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27855/head:pull/27855

PR: https://git.openjdk.org/jdk/pull/27855