🎨 Fix rendering API to handle annotation classes

[tim-evans]

This PR changes the rendering API so annotation classes can be reused in the render hooks.

Previously, when an annotation was rendered, it would be called with the attributes, that stripped all type information:

import Renderer from '@atjson/renderer-hir';
import { HIRNode } from '@atjson/hir';

export default class TestRenderer extends Renderer {
  *image(attrs: any): IterableIterator<any> {
    return `![${attrs.description}](${attrs.src})`;
  }
}

Now, classes can be reused:

import { ObjectAnnotation } from '@atjson/document';
import Renderer from '@atjson/renderer-hir';

class Image extends ObjectAnnotation {
  static vendorPrefix = 'test';
  static type = 'image';
  attributes!: {
    description: string;
    src: string;
  };
}

export default class TestRenderer extends Renderer {
  *image(image: Image): IterableIterator<any> {
    return `![${image.attributes.description}](${image.attributes.src})`;
  }
}

In addition! There is now metadata associated on annotations passed to renderers for tricky rendering scenarios like markdown, which will hopefully remove the need for fully-custom renderers! ✨ (For context, this is currently being done here and used for ambiguous nesting of bold and italic and adjacent lists of the same type)