Add executionContext/interrupt API command

[4e6]

Pull Request Description

Implement the executionContext/interrupt API command that forcibly stops the program execution.

Important Notes

Checklist

Please include the following checklist in your PR:

• The documentation has been updated if necessary.
• All code conforms to the
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• All code has been tested:
  • Unit tests have been written where possible.
  • If GUI codebase was changed: Enso GUI was tested when built using BOTH
    ./run ide build and ./run ide watch.

[4e6]

Our runtime tests are sequential, i.e. all the commands sent to the engine are executed in sequence. It is a very useful property when testing the code because it prevents all kinds of race conditions.
Unforutnately, you cannot test the program interruption with the sequential flow because you need to send an interruption command while the previous command (execute program) is still in progress. That's why there is a new suite.

[JaroslavTulach]

I haven't found the "forcibly stop program execution" implementation - I assume it already existed and this PR just makes it available via the protocol, right?

[hubertp]

probably needs an update about ContextDoesNotExist?

[4e6]

I haven't found the "forcibly stop program execution" implementation - I assume it already existed

@JaroslavTulach under the hood the logic calls ThreadManager.interruptThreads() method. I assume that this is the way to interrupt the program execution.