RFR: 8309334: ProcessTools.main() does not properly set thread names when using the virtual thread wrapper

[Chris Plummer]

Normally when a virtual thread wrapper is used to run a test, the main thread is renamed to "old-m-a-i-n" and the new virtual thread that will act as the main thread is named "main". Neither is being done by `ProcessTools.main()`. This can cause problems for tests that expect the main thread that the test is running in to be called "main". It is instead left unnamed. This is causing the following 4 tests to fail:

com/sun/jdi/JdbMethodExitTest.java
com/sun/jdi/JdbStepTest.java
com/sun/jdi/JdbStopThreadTest.java
com/sun/jdi/JdbStopThreadidTest.java

These tests also fail due to [JDK-8309397](https://bugs.openjdk.org/browse/JDK-8309397), which will be fixed after this CR, and also com/sun/jdi/JdbMethodExitTest.java fails due to [JDK-8309396](https://bugs.openjdk.org/browse/JDK-8309396), which will also subsequently be fixed.

Note this fix messed up one runtime test. It was expecting an exception message to mention the "main" thread rather than "old-m-a-i-n". Loosening the exception message matching pattern a bit solved the problem.

Testing was done by running all of tier1 and tier5.

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

Commit messages:
 - when using virtual threads, properly name the main threads

Changes: https://git.openjdk.org/jdk/pull/14292/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14292&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309334
  Stats: 11 lines in 2 files changed: 5 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/14292.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14292/head:pull/14292

PR: https://git.openjdk.org/jdk/pull/14292