This is a plugin for for the CKEditor WYSIWYG.
The Media Link (labeled "Teaser Link Box" in the UI) is another custom CKEditor plugin. The output is a standard media object that shows an image to the left of a title and body
The markup within CKEditor will be:
<media-link url="#">
<div slot="image"></div>
<div slot="title">Title</div>
<div slot="content"><p>Content</p></div>
</media-link>A Text filter or web component on the frontend can then transform this markup into whatever is desired.