Collection: Introduce Collection Item Ref extension type

[madsrasmussen]

Building of top of: #20954 . Please review first.

Following in the steps of the Collection Item Card extension point, this PR brings a Collection Item Ref extension point. The extension point follows the exact same interfaces but offers a different rendering opportunity. The PR also introduces a Base Element and Manifest Type to work for both the card and ref types.

Manifest Example

{
  type: 'entityCollectionItemRef',
  alias: 'My.EntityCollectionItemRef.CustomType',
  name: 'My Custom Type Entity Collection Item Ref',
  element: () => import('./my-custom-type-collection-item-ref.element.js'),
  forEntityTypes: ['my-custom-type'],
}

Basic Element Example

@customElement('my-custom-type-collection-item-ref')
export class MyCustomTypeCollectionItemRefElement extends UmbLitElement {
	
  @property({ type: Object })
  item = false;

  @property({ type: Boolean })
  selectable = false;

  @property({ type: Boolean })
  selected = false;

  @property({ type: Boolean })
  selectOnly = false;

  @property({ type: String })
  href?: string;

  #onSelected(event: CustomEvent) {
    if (!this.item) return;
    event.stopPropagation();
    this.dispatchEvent(new UmbSelectedEvent(this.item.unique));
  }

  #onDeselected(event: CustomEvent) {
    if (!this.item) return;
    event.stopPropagation();
    this.dispatchEvent(new UmbDeselectedEvent(this.item.unique));
  }

  override render() {
    if (!this.item) return nothing;
    return html` <div>My Ref rendering</div> `;
  }

  static override styles = [css``];
}