Introduce low-level JFR events

[leonard84]

Motivation

Currently, junit-platform-jfr provides events that are observable to standard listeners.

However, it can't provide insights into low-level events, such as the exclusive resource locks.

Previously, it was decided to only introduce JFR via an optional module because it was not supported until JDK 11. A lot has changed since: JFR has been backported to openjdk8, and all current distributions support it. Plus, JDK 9 and 10 have been EOL for a long time.

Furthermore, there is the https://github.com/gradle/jfr-polyfill project that provides a no-op implementation that prevents any crashes due to ClassNotFoundError.

Deliverables

• Move JFR events into the platform core
• Add additional low-level events, e.g., for resource locks

[marcphilipp]

TODO: Double-check if OpenJ9 also supports JFR

[sormuras]

Not yet, it seems:

• Implement Java diagnostic utilities eclipse-openj9/openj9#4655

[leonard84]

OpenJ9 should work with jfr-polyfill. The question is whether you'd want to add it as a default dependency, or if OpenJ9 users should add it themselves.

[marcphilipp]

As a first step, we should add a CI build using OpenJ9 to run tests. I'll see to that.

[marcphilipp]

As a first step, we should add a CI build using OpenJ9 to run tests. I'll see to that.

Done in #3768