prefer-regexp-test should only apply to strings

[DamienCassou]

The rule prefer-regexp-test triggers an error for:

criteria.match(item)

but criteria isn't a string it is an instance of my own class. I don't want the rule to trigger.

[fisker]

I don't think we can do anything, we can't know the types.

[DamienCassou]

Then I guess the rule shouldn't change the code. Maybe just provide suggestions as discussed in #441?

[fisker]

If we want to disable auto-fix, I'd prefer to add an option {fix: false}, but still auto-fix by default.

[privatenumber]

This autofix also broke my code.

I think the autofix should only apply if it can confidently determine that the type is a RegExp (e.g. declared as a const in the same file).