RFR: 8370905: Update vm.defmeth tests to use virtual threads [v2]

[Leonid Mesnik]

> The vm.defmeth stress tests should use
> `TestThreadFactory.newThread()`
> to start virtual threads if test thread factory is used.

Leonid Mesnik has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - removed setName
 - Merge branch 'master' of https://github.com/openjdk/jdk into 8370905
 - 8370905: Update vm.defmeth tests to use virtual threads

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28048/files
  - new: https://git.openjdk.org/jdk/pull/28048/files/4d6d6786..cee025e5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28048&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28048&range=00-01

  Stats: 319462 lines in 2913 files changed: 206267 ins; 71095 del; 42100 mod
  Patch: https://git.openjdk.org/jdk/pull/28048.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28048/head:pull/28048

PR: https://git.openjdk.org/jdk/pull/28048