prepareMeta function similar to prepareStory

[JReinhold]

This PR implements a prepareMeta function, that similar to prepareStory, combines project annotations with component annotations, but without story annotations.

This is exposed in the useOf hook in blocks, that is then used by the Description block to render descriptions.

This is just a refactor, no stories should change because of this.

[JReinhold]

one could argue that this functionality should be directly in DocsContext.resolveModuleExport and not in useOf.

I'm indifferent.

[tmeasday]

We can always change it later if we need it higher up.

[tmeasday]

I think we should split this a little more so it looks like:

function prepareStory(..) {
  const partial = prepareAnnotations(...);

  const unboundStoryFn = () => {....}
  // ...

  return {
     ...partial,
     id: ..,
     name: ...,
     unboundStoryFn,
     // ...
  };
}

That way we aren't doing all the story function preparation for no reason with a mocked function.

[tmeasday]

We shouldn't set an id

[JReinhold]

I'm not sure about that. componentAnnotations have ids, and all of the tests for prepareStory pass in an id as the componentAnnotations id.

I agree that we shouldn't set a fake one, we should just use the one from componentAnnotations, I've changed that.

[tmeasday]

We can always change it later if we need it higher up.

[JReinhold]

@tmeasday I refactored it so the story-specific stuff only happens in prepareStory as well as created actual types for PreparedMeta.
I couldn't completely get rid of "fake" story identifiers (id, name, story) because we need to pass them to enhancers to build argTypes, etc.

[tmeasday]

Excellent, thanks @JReinhold