fix: Disable nested embedding fully

[juliushaertl]

We want to prevent nesting interactive widgets, so this will ensure that we know about that text is rendered as an embedding with nextcloud/server#44012

Follow up to check

• Check if we can just use inject in the paragraph component if we use the viewer vue instance

[skjnldsv]

One would argue that this is not an official Viewer prop yet 🙈
But it make sense, we'll need to consider this for Viewer 3

[max-nextcloud]

Just two minor comments. One of them might point at a conceptual issue though... Do we want to render the previews inside embedded content non-interactive or not at all?

If we don't render the Preview nothing will be shown - not even the embedded link. So maybe we leave out the Preview nodes all together then and at least show the link?