Warn when Mutator in directive does not exist

[Giovds]

Closes #3812

When a directive references an unknown Mutator, log a warning that this directive is not used.

Mutated code

const compare = (a, b) => {
  // Stryker disable HelloThere
  // Stryker disable next-line Equality: Wrong Mutator name
  return a - b >= 0 ? 1 : -1;
}

module.exports = { compare };

module.exports = { compare };

Cli

[Giovds]

A couple of questions/issues I still have:

1. I've made an assumption here: https://github.com/stryker-mutator/stryker-js/pull/3842/files#diff-87b4b61b8bd5767c34cf6b141cc3721b722a730e884627e7adc127c8449a07b4R79. Is this correct?
2. It probably is confusing that the ignored mutant in the HTML view shows a diff on the comment but has no 'addition line'.
3. It seems that the line number is off by 1. There is a toBabelLineNumber() method which adds 1 to the line number. Should this be used to re-convert the lines to their original numbers?

@nicojs Thoughts?

[nicojs]

It is pretty clever to see how you report mutants for unused stryker directives, but I don't think it's a good idea :/. Mutants are mutations in the code, not unused directives.

I think logging them as a warning is good enough for now. For example, users might want Stryker to fail fast instead of showing them in the report 🤷‍♀️.

[nicojs]

Looking good! 🤩 , still some stuff left.

[nicojs]

This looks awesome; just a couple of remarks left. Let me know if you need more help.

[nicojs]

Thanks! 🎉