RFR: 8355071: Fix nsk/jdi test to not require lookup of main thread in order to set the breakpoint used for communication [v2]

[Chris Plummer]

> Remove the need for many nsk/jdi tests to discover the main thread, resulting in the test needing to be run with includevirtualthreads=y. Details in first comment.
> 
> Tested with all tier2, tier3, and tier5 svc tests

Chris Plummer has updated the pull request incrementally with one additional commit since the last revision:

  Add new settingBreakpoint() API for when thread is null

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24768/files
  - new: https://git.openjdk.org/jdk/pull/24768/files/934cde70..2b019b9d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24768&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24768&range=00-01

  Stats: 22 lines in 1 file changed: 21 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24768.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24768/head:pull/24768

PR: https://git.openjdk.org/jdk/pull/24768