Add action delegation

In #90 we added filter delegation, in #102 we proposed locator delegation. The final piece of the puzzle is action delegation! Action delegation kind of already exists today:

HTML.extend('calendar')
  .selector('.calendar')
  .actions({
    async open(interactor) {
      await interactor.find(Button('Open').click());
    }
  });

The idea here is to align this with the filter syntax, to achieve something like the following:

HTML.extend('calendar')
  .selector('.calendar')
  .actions({
    open: Button('Open').click()
  });

Which would have identical behaviour.

The problem is that actually implementing this is probably very difficult, and will require some deep rethinking of interactions to make this possible.

No files or tests are named. Start by tracing the existing .actions implementation and the filter delegation from #90, then compare the locator delegation proposal in #102; done means the shorthand action syntax has identical behavior to the current async implementation.