Render PDF attachments

[ChristophWurst]

Is your feature request related to a problem? Please describe.

Ref #5988

Describe the solution you'd like

No response

Describe alternatives you've considered

No response

Additional context

No response

[ChristophWurst]

Judging by https://github.com/nextcloud/files_pdfviewer/tree/master/src there is some boilerplate code we need to get pdfjs into Vue.

On the npm registry I could only find a rather outdated wrapper for Vue: https://github.com/FranckFreiburger/vue-pdf

[ChristophWurst]

Another possibility is to use <object> or <embed>, if we can safely assume that all our supported browsers can render PDF natively: https://stackoverflow.com/questions/4853898/display-pdf-within-web-browser.

[ChristophWurst]

nextcloud/viewer#1338 for the Viewer adaptation.

[ChristophWurst]

nextcloud/files_pdfviewer#646 for the PDF viewer part