RFR: 8291429: java/lang/Thread/virtual/ThreadAPI.java timed out on single core system [v2]

[Alan Bateman]

> This is a test only change for two tests for virtual threads that hang/timeout on single core systems. The two tests involve pinning and require at least two carrier threads. The test lib used by these tests is updated to define a new method that ensures parallelism is at least a given value and both tests are updated to use this. There are a number of tests in the debugger area that may potentially use this in the future.

Alan Bateman 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 four additional commits since the last revision:

 - Replace try-with-resource with try-finally
 - Merge
 - Make close idempotent
 - Initial commit

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10562/files
  - new: https://git.openjdk.org/jdk/pull/10562/files/5ac95695..bc2c3f13

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10562&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10562&range=00-01

  Stats: 1769 lines in 125 files changed: 861 ins; 452 del; 456 mod
  Patch: https://git.openjdk.org/jdk/pull/10562.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10562/head:pull/10562

PR: https://git.openjdk.org/jdk/pull/10562