Preview Improvements

Over time, with several modifications to preview elements, preview component has become complex and inefficient for the user.

For the developer :

• It can be confusing to understand which type of strategy to follow to create a document type preview. The pipeline tries to find a specific adapter for the document type. If not found and the document type has a blobholder adapter or as 'file'/'files' schema, it will present that blob mimetype preview.
  If there is no specific mimetype preview contribution, it will default on a conversion that tries to convert from any to html.

This last convertor tries to convert directly to html or first to PDF and from there to html.

This can be hard to comprehend and to select the best option per case.

For the user:

• the last fallback will be to convert to PDF and afterwards to HTML. The preview should be html in our case, but is preferable a PDF viewer that we already have than a conversion to plain html.
• Preview action can be redundant to document view.
• Blob preview can also be redundant.
• Blob preview could be viewed without fullscreen.

Streamline the preview component to simplify it with a clear pipeline with less, but more specific fallbacks. PDF should be considered a goal conversion and wrap in html viewer. Blobs can be previewed in document view. Preview action should be just a full screen action on any preview.