Add support for loading Drupal JavaScript libraries via custom elements

Problem/Motivation

When rendering Drupal render arrays to CustomElements via `setSlotFromRenderArray()`,
the `#attached` libraries are lost. The render array is processed through
`renderInIsolation()` which renders the HTML markup, but the attached libraries
(JS) are not captured in the CustomElement structure.

This is problematic for decoupled frontends that need to load Drupal JavaScript
libraries for functionality like:
- Form states/conditional fields (`core/drupal.states`)
- Autocomplete fields (`core/drupal.autocomplete`)
- Various widgets and behaviors

Proposed resolution

When rendering render arrays to custom elements, emit ``
elements as part of the slot content:

1. Capture `#attached` before rendering
2. Resolve library dependencies in correct load order
3. Generate `drupal-library-{name}` custom elements with JS file paths
4. Prepend library elements to slot content (before markup)
5. Include `drupalSettings` as props when present

Example output:

{
  "element": "drupal-markup",
  "slots": {
    "default": [
      { "element": "drupal-library-core-jquery", "props": { "js": [...] } },
      { "element": "drupal-library-core-drupal-states", "props": { "js": [...] } },
      "<div class=\"form-wrapper\">...</div>"
    ]
  },
  "props": { "drupalSettings": {...} }
}