SA: Add new stress test that tests getting the stack trace of an active thread

JDK-8243455 was due to many tests trying to get the stack trace of a active thread, and then look for a specific frame in the stack trace. The problem is thread might be in a state that doesn't allow SA to get the stack trace, causing the test to fail.

JDK-8243455 is being fixed by having the tests instead use the stack trace of a thread that is not active. However, doing this also eliminates some vital SA testing of active thread stack traces. Although SA might not always be able to get the stack trace, it should not hang, assert, or throw various exceptions, all of which have been issues in the past, and a number of fixes have been put in place for.

This task will include a new test that stresses getting the stack trace of active threads, making sure no SA errors result from doing so.