RFR: 8303703: Add support of execution tests using virtual thread factory jtreg plugin [v2]

[Leonid Mesnik]

> The plugin which support execution of test's main method in separate virtual thread is added.
> The plugin is built as a part of test image and might be used in testing by adding JTREG_TEST_THREAD_FACTORY=Virtual option.

Leonid Mesnik has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 34 commits:

 - updated virtual plugin impl
 - Merge branch 'master' of https://github.com/openjdk/jdk into ttf-build
 - opts updated
 - deps updated
 - fixed is to are
 - copyrights fixed
 - fix
 - Merge branch 'master' of https://github.com/openjdk/jdk into ttf-build
 - problemlists deleted.
 - Merge branch 'master' of https://github.com/openjdk/jdk into ttf-build
 - ... and 24 more: https://git.openjdk.org/jdk/compare/e3ece365...31e3cbd1

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Changes: https://git.openjdk.org/jdk/pull/13432/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13432&range=01
  Stats: 174 lines in 9 files changed: 171 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13432.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13432/head:pull/13432

PR: https://git.openjdk.org/jdk/pull/13432