Do not request previews if providers are disabled

[juliusknorr]

When preview providers are disabled for certain types (e.g. video) we should not even try to fetch previews as this may add extra load on the server.

We could expose supported mime types filtered by the provider support as initial state and use that as an allow list for fetching previews.

[juliusknorr]

@skjnldsv I remember some discussion about this (maybe with viewer) but could not find any reference. Do you know if we have a similar thing already somewhere else?

[skjnldsv]

In Viewer we use the hasPreview dav property, and load the full ressource if not available.
https://github.com/nextcloud/viewer/blob/61f7935dd393b0c630a97beec18286ac591a9676/src/mixins/PreviewUrl.js#L69-L87

[szaimen]

Do you mean this?
https://github.com/nextcloud/viewer/blob/62f1c1613f94319c24f749fddfab58a1a65c0a5e/lib/Listener/LoadViewerScript.php#L55

[skjnldsv]

Do you mean this? nextcloud/viewer@62f1c16/lib/Listener/LoadViewerScript.php#L55

This disable the registration entirely :)
This is a step further than just not requesting previews