Adding support for JFR ExecutionSample event.

[jovanstevanovic]

This PR is introducing the ExecutionSample event and adds one test for the thread repository.

Event signature:

@name("jdk.ExecutionSample")
@category({"Java Virtual Machine", "Profiling"})
@Label("Method Profiling Sample")
@description("Snapshot of a threads state")
class ExecutionSample extends jdk.jfr.Event {
@Label("Start Time")
@timestamp("TICKS")
long startTime;

@Label("Thread")
Thread sampledThread;

@Label("Stack Trace")
StackTrace stackTrace;

@Label("Thread State")
String state;
}

[oubidar-Abderrahim]

Hi, @jovanstevanovic Thank you for contributing to GraalVM, could you please provide answers to the following questions?

1. Is your PR complete and ready for review?
2. Did you have a conversation about these changes with some team members and you would like for them to review this as they have more context? please mention them
3. Does your changes rely on other changes made in a separate PR? if yes please link it to this one

[jovanstevanovic]

Hi, @jovanstevanovic Thank you for contributing to GraalVM, could you please provide answers to the following questions?

1. Is your PR complete and ready for review?

2. Did you have a conversation about these changes with some team members and you would like for them to review this as they have more context? please mention them

3. Does your changes rely on other changes made in a separate PR? if yes please link it to this one

Hi, @oubidar-Abderrahim!

1. It has one TODO left in the code because I was not sure how to do that.
2. I talked with @christianhaeubl about these changes, and now, I'm waiting for his review.
3. No, there are no other PRs linked to this one.

[christianhaeubl]

Only minor comments, everything else looks good.