Duplicate add-ons shown for VLC
Moving this to a new issue from !598 (comment 1018324)
When an application is updated over time to use a new runtime, its extension points can change. We should only show the user extensions compatible with the version they have installed or will install, rather than all available versions, which are displayed as duplicates.
This will require adding API to libflatpak (which I'm working on) unless we want to manually parse the extension information from the metadata, which is a bit hairy.