Implements custom scheduler event tracing

[franz1981]

Similarly to the JMC threads state tab, would be great to implements telemetry for scheduling events
i.e. running, descheduled (with reasons: blocked on I/O, parked/monitorEnter/yield), scheduled/ready to run - in order to present a timeline of such, per carrier or scheduler instance.

We need to check first if JMC doesn't already do it and if JFR doesn't provide a mix of existing events (on thread state change/virtual threads events) which would provide the same info.
If not, we need to decide how to visually present it - possibly reusing something existing (JMC? Or others...).

[franz1981]

It looks like JMC can do it too - but I have to verify it.
In the meantime https://gist.github.com/yawkat/5b952e47ced9e062f8f241d775a67f08 @yawkat shared a way to present custom JFR events which can be used to understand if the scheduler is well behaving