compiler/tests: dynamic events: validate handler before executing

[ghost]

Fixes #4087, #4090.

Background
Dynamic events are callbacks that reside in a variable instead of directly pointing to a function and are emitted by the compiler when the variable is mutated or assigned in some way.

I noticed in #4087 that the dynamic event handler test case was throwing exceptions, but still passing.
Further investigation uncovered an issue where we were not properly handling exceptions in the run-time during testing. This led to filing #4090 after the root cause of the exception turned out to the lack of callback validation inside the proxy function used for dynamic events.

This pull request addresses both of these issues along with adding much more coverage for dynamic events.

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• It's really useful if your PR relates to an outstanding issue, so please reference it in your PR, or create an explanatory one for discussion. In many cases features are absent for a reason.
• This message body should clearly illustrate what problems it solves. If there are related issues, remember to reference them.
• Ideally, include a test that fails without this PR but passes with it. PRs will only be merged once they pass CI. (Remember to npm run lint!)

Tests

• Run the tests tests with npm test or yarn test)

[ghost]

@Conduitry,
I dropped the codegen tests because they aren't needed and broke after some other commits were added. I did leave the update to the existing test though.

[tanhauhau]

Suggested change

	err = e.message;
	err += e.message;

should concat all the error messages

[ghost]

Thanks for the review, I'll push up changes after the holiday or feel free to push a commit sooner if needed.