RFR: 8313654: Test WaitNotifySuspendedVThreadTest.java timed out

[Leonid Mesnik]

Test might times out if it suspend thread before it starts breakpoint event handler.
The fix is to replace sleep with better synchronization and suspend virtual thread only when it runs native code.

Also, the completed monitor is acquired earlier to avoid racing when completing test.

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Commit messages:
 - 8313654: Test WaitNotifySuspendedVThreadTest.java timed out

Changes: https://git.openjdk.org/jdk/pull/15196/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15196&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313654
  Stats: 35 lines in 2 files changed: 14 ins; 19 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15196.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15196/head:pull/15196

PR: https://git.openjdk.org/jdk/pull/15196