RFR: 8338714: vmTestbase/nsk/jdb/kill/kill001/kill001.java fails with JTREG_TEST_THREAD_FACTORY=Virtual. [v2]

[Chris Plummer]

> This test fails after [JDK-8338713](https://bugs.openjdk.org/browse/JDK-8338713) when using JTREG_TEST_THREAD_FACTORY=Virtual. The test uses JVMTI StopThread on a thread expecting it to be mounted. Before [JDK-8338713](https://bugs.openjdk.org/browse/JDK-8338713) it would be mounted because it was blocked on a syncrhonized, which resulted in the thread being pinned. After [JDK-8338713](https://bugs.openjdk.org/browse/JDK-8338713) this is no longer the case and the virtual thread has unmounted. This causes JVMTI StopThread to fail with JVMTI_ERROR_OPAQUE_FRAME because it only supports mounted virtual threads.
> 
> Fixed by using the VThreadPinner class to make sure the virtual threads remains pinned, and therefore mounted.
> 
> Testing:
> 
> - [x] Ran jdb tests locally in both virtual thread mode and platform thread mode.
> - [x] tier1
> - [x] tier2 svc
> - [x] tier5 svc

Chris Plummer has updated the pull request incrementally with one additional commit since the last revision:

  Rename run1() to test()

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22620/files
  - new: https://git.openjdk.org/jdk/pull/22620/files/47ccd8db..d801499f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22620&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22620&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/22620.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22620/head:pull/22620

PR: https://git.openjdk.org/jdk/pull/22620