Support inheritance for `methods`, `targets`, `values`, etc.

[Marco Roth]

It's common for Stimulus controllers to inherit some behaviour from an (abstract) base controller.

Currently the inherited methods, targets, values, etc. aren't provided on the child controller.

Like:

// base_controller.js

import { Controller } from "@hotwired/stimulus"

export default class extends Controller {
  static targets = ["base"]
}

// specfic_controller.js

import BaseController from "./base_controller"

export default class extends BaseController {
  static targets = ["specific"]
}

The specific controller should now have both the base and specific target.