Utilize ffmpegthumbs or ffmpegthumbnailer for thumbnails for video files

[rdrms]

I think it would be a good idea if we could have thumbnails in the file manager for video files, especially mp4, webm, and mkv files that I interact with a lot.

KDE has one solution for this: ffmpegthumbs. Other desktops can use "ffmpegthumbnailer" to get thumbnails in their respective file manager. The solution used by both of these are the same, they pass a video file through ffmpeg to create the thumbnail.

If we could reuse the same solution it would be great! From what I understand from the code, it seems that it is using its own thumbnailer built into the file manager and not any third party ones.