RFR: 8355569: Some nsk/jdi tests can glean the "main" thread by using the ClassPrepareEvent for the debuggee main class [v3]

[Chris Plummer]

> As part of the work for [JDK-8353955](https://bugs.openjdk.org/browse/JDK-8353955) I am reducing the number of tests that need to be run with includevirtualhreads=y due to using JDI to lookup threads in the debuggee. There are many tests that lookup the "main" thread. They can instead glean the "main" thread from the ClassPrepareEvent for the debuggee main class. Some tests already wait for this ClassPrepareEvent, and can take advantage of it. Most do not, but can be made to do so. The easiest way to do this for many of the tests is to wait for the event in Debuggee.prepareDebuggee() after having called Debuggee.bindToDebuggee(). For tests that don't call Debuggee.prepareDebuggee(), waiting for the ClassPrepareEvent was added after the bind. This doesn't seem to have any ill affect on the tests.
> 
> Tested by running all nsk/jdi tests, including all tier2, tier3, and tier5 nsk/jdi testing.

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

  found one more test to fix

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24867/files
  - new: https://git.openjdk.org/jdk/pull/24867/files/060c8d3d..a95698df

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24867&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24867&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/24867.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24867/head:pull/24867

PR: https://git.openjdk.org/jdk/pull/24867