[bug]: SlotController issue in `getSlotted()` not returning elements as expected

[zeroedin]

getSlotted() should return the assignedElements() of a slot. It's usage downstream in rh-subnav was returning an empty array []. Needs more investigation.

For now, removing the SlotController from rh-subnav is lighter weight for the simple usage in rh-subnav rather than adding the whole dependency of SlotController.

[zeroedin]

After further investigation, we can change the implementation to be async and return a promise after the component updates to read the slotted content.

 <slot @slotchange="this.#onSlotchange()"></slot>

  async #onSlotchange() {
    await this.updateComplete;
    const elements = await this.#slots.getSlottedElements();
  }

  public async getSlottedElements(name?: string | null): Promise<Element[]> {
    await this.host.updateComplete;
    // get slot content
    const slot = this.#slotRecords.get(name ?? SlotController.default);
    return Promise.resolve(slot?.elements ?? []);
  }

[zeroedin]

Current getSlotted returns only Elements, and it wants to for every slot given in the params. I can't think of a reason to do this, and we aren't currently using it anywhere (outside rh-subnav) where it was broken.

Should we deprecate getSlotted() and replace with getSlottedElements() and getSlottedNodes()

Modify SlotRecord to include get nodes():

  get elements() {
    return this.slot?.assignedElements?.();
  }

  get nodes() {
    return this.slot?.assignedNodes?.();
  }

Include a similar method to getSlottedElements

  public async getSlottedNodes(name?: string | null): Promise<Node[]> {
    await this.host.updateComplete;
    const slot = this.#slotRecords.get(name ?? SlotController.default);
    return Promise.resolve(slot?.nodes ?? []);
  }

This would more closely match the use of assignedElements() and assignedNodes()

We could also just deprecate the getSlotted() method completely and remove it in favor of just using assignedElements or assignedNodes. Not sure there is a benefit to mimicking that API in the controller.