RFR: 8316924: java/lang/Thread/virtual/stress/ParkALot.java times out

[Alan Bateman]

A test only change to a stress test for virtual thread parking/unparking to limit execution time on a larger systems. Right run, the test bashes parking/unparking for 1, 2, 3, ... up to the number of half the hardware threads. It is changed to limit it to 4 iterations. It is also dialed down for debug builds as they may run with -XX:+VerifyContinuations which is an expensive assert (but an important one for tests like that).

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/15940/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15940&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316924
  Stats: 5 lines in 1 file changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/15940.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15940/head:pull/15940

PR: https://git.openjdk.org/jdk/pull/15940