option: list subclass names

[bennypowers]

We should provide an option that lists (string) subclass names, so that

export class IsReallyALitElement extends FooElement {
  /*...*/
}

lints up with our plugin

[43081j]

probably can re-use the same logic eslint-plugin-wc uses:

"settings": {
  "wc": {
    "elementBaseClasses": ["MyElement"]
  }
}

one idea is that we could use the same detection as eslint-plugin-wc: look for a customElement decorator or JSDoc on the class we're in. then if we see it has a render method and makes use of html, maybe we assume its a lit element?

bit of an awkward one though, lot of guesswork 😬

may be better to just do the base class stuff