Update: improve suggestion testing experience

[bradzacher]

Previously you had to explicitly set suggestions: undefined, or omit the property.
I hate writing undefined in my code, but I also prefer to be explicit in my tests, and explicitly say "I expect no suggestions".

This just lets a user pass any falsey value, or an empty array.
The rule tester will interpret any of these values as "I expect no suggestions".

I.e. these will now be equivalent:

ruleTester.run("suggestions-basic", rule, {
  valid: [],
  invalid: [
    // previously only allowed:
    {},
    {
      suggestions: undefined,
    },
    // now also allows
    {
      suggestions: [],
    },
    {
      suggestions: null,
    },
    {
      suggestions: false,
    },
  ],
});

[kaicataldo]

This seems like a good idea to me. I'll champion this.

[platinumazure]

Note to merger: This should be an "Update:" as we are regarding this as an enhancement.