Allow attachments in media processor

Problem/Motivation

Libraries are not attached to rendered media tokens.

Steps to reproduce

- Install Drupal 11 standard profile
- Install modules patternkit_example, patternkit_media_library, layout_builder
- Configure a content type to use Layout Builder
- On /admin/config/development/settings, enable "Do not cache markup" and "Twig development mode" (this makes debugging easier)
- On /admin/config/development/performance, disable CSS aggregation (this makes verifying easier in the final step)
- Create a node. On that node's Layout tab, insert block of type "[Patternkit] Media image embed".
- Select an image for that block (or upload new one).
- Save the layout.
- Inspect the image element. Notice that the Twig template rendering that image is core/modules/system/templates/image.html.twig
- Edit that Twig template. Add this line, to attach a new Claro library: {{ attach_library('claro/form-two-columns') }}
- Reload the node's page.
- Inspect the page source. Expect to find reference to core/themes/claro/css/layout/form-two-columns.css. However, you won't see it because Patternkit's media processor does not allow attachments to "bubble up" to the render system.

Proposed resolution

See MR https://git.drupalcode.org/project/patternkit/-/merge_requests/154.

When applied, you should see the attached library's assets in the page source (e.g., form-two-columns.css from the above example).

Remaining tasks

Write tests?

User interface changes

None

API changes

None

Data model changes

None