fix(ViewerComponent): use MarkdownContentEditor for readonly views

[mejo-]

Also pass the fileId to the component. This adds support for displaying images and attachments in the read-only view.

Fixes: #6267

I tested this PR with

• Text in Text (via preview link) in Viewer
• Text in Talk (via preview link)
• Text in Collectives (both view and edit mode)

The editor CSS includes (prosemirror.css and print.css) were missing in MarkdownContentEditor, which resulted in broken view in Talk - probably because that was the only scenario where no second editor was loaded that the same time.

🖼️ Screenshots

🏚️ Before	🏡 After

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits

[juliusknorr]

cypress failure seems related:

  1) Versions
       View versions with close timestamps:
     AssertionError: Timed out retrying after 10000ms: Expected to find element: `.viewer__content #read-only-editor`, but never found it.
      at Context.eval (http://localhost:8081/__cypress/tests?p=cypress/e2e/versions.spec.js:104:12)

  2) Versions
       View versions:
     AssertionError: Timed out retrying after 10000ms: Expected to find element: `.viewer__content #read-only-editor`, but never found it.
      at Context.eval (http://localhost:8081/__cypress/tests?p=cypress/e2e/versions.spec.js:123:12)

  3) Versions
       Compare versions:
     AssertionError: Timed out retrying after 10000ms: Expected to find element: `.viewer__content #read-only-editor`, but never found it.
      at Context.eval (http://localhost:8081/__cypress/tests?p=cypress/e2e/versions.spec.js:144:12)

[mejo-]

cypress failure seems related:

Indeed, fixed now.

[mejo-]

/backport to stable30