Improve handling of prevent download permission

With https://github.com/nextcloud/server/pull/32482 using the viewer only works for apps like Collabora as for other filetypes like images the download to the users browser would be blocked if the download permission is removed from a share.

The error message for that is quite generic that it failed to load the file. In oder to improve the user experience, it would make sense to implement support for this in the viewer app.

Suggested implementation

In addition to the existing list of mime types for a handler, Collabora could pass over a list of mime types for "secure view". With this list, the viewer could check on the share attribute to see if download is disabled and then either show a proper fitting error message or still load the file if the handler supports the current mime type.

Any objections @skjnldsv @Raudius @CarlSchwan ?

Start by reviewing the viewer's existing handler MIME type list and how it reads the share's download permission. Trace the Collabora handler integration and determine how secure-view MIME types should be passed and checked. Done means supported files load when downloads are disabled, while unsupported files show a specific error instead of the generic load failure.