RFR: 8359827: Test runtime/Thread/ThreadCountLimit.java should run exclusively

[SendaoYan]

Hi all,

The test runtime/Thread/ThreadCountLimit.java was observed fails when run with other tests. The test start subprocess with [shell prefix command](https://github.com/openjdk/jdk/blob/master/test/hotspot/jtreg/runtime/Thread/ThreadCountLimit.java#L82) `ulimit -u 4096` which intend to limite the usage of thread number. But this will cause test fails when this test run with other tests. I create a demo to demonstrate that.

I start a java process which will create 5k threads, and then I can not start new java process with prefix `ulimit -u 4096` on the same machine.

<img width="1573" height="182" alt="image" src="https://github.com/user-attachments/assets/8dd53ade-cad7-4a2f-b5d9-d4b2d200b728" />


[ManyThreads.java.txt](https://github.com/user-attachments/files/21324354/ManyThreads.java.txt)

So it's necessary to make this test run sperately to make this test success.
Change has been verified locally, test-fix only, risk is low.

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Commit messages:
 - add test/hotspot/jtreg/runtime/Thread/stress/TEST.properties
 - 8359827: Test runtime/Thread/ThreadCountLimit.java should run exclusively

Changes: https://git.openjdk.org/jdk/pull/26401/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26401&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8359827
  Stats: 2 lines in 2 files changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/26401.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26401/head:pull/26401

PR: https://git.openjdk.org/jdk/pull/26401