[jdk21u-dev] RFR: 8355071: Fix nsk/jdi test to not require lookup of main thread in order to set the breakpoint used for communication

[Goetz Lindenmaier]

I backport this to keep the tests up to date and make later backports clean.

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Commit messages:
 - Backport b7e8952ad6def4ebae8c8c3c04cf6793f472b029

Changes: https://git.openjdk.org/jdk21u-dev/pull/2404/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2404&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8355071
  Stats: 1996 lines in 189 files changed: 73 ins; 1534 del; 389 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2404.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2404/head:pull/2404

PR: https://git.openjdk.org/jdk21u-dev/pull/2404