RFR: 8339638: Update vmTestbase/nsk/jvmti/*Field*Watch tests to use virtual thread factory

[Leonid Mesnik]

Field watch tests updated to be executed with virtual threads when virtual test thread factory enabled.I added 
jdk.test.lib.thread.TestThreadFactory
to created test threads so they support virtual thread factory jtreg plugin.

It might makes sense to use it in different tests so virtual threads are tests more extensively.
There is JDIThreadFactory in nsk/sharejdi which I copied. I am going to update JDI tests to use jdk.test.lib.thread.TestThreadFactory
later.

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Commit messages:
 - 8339638: Update vmTestbase/nsk/jvmti/*Field*Watch tests to use virtual thread factory

Changes: https://git.openjdk.org/jdk/pull/20897/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20897&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339638
  Stats: 75 lines in 5 files changed: 63 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/20897.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20897/head:pull/20897

PR: https://git.openjdk.org/jdk/pull/20897