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

[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.

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Commit messages:
 - update copyrights
 - Get debuggee main thread from ClassPrepareEvent for debuggee main class.

Changes: https://git.openjdk.org/jdk/pull/24867/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24867&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8355569
  Stats: 162 lines in 36 files changed: 74 ins; 15 del; 73 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