Our migrators all return resources if they find the bare minimum to indicate that those resources exist - for example, we return the Safari bookmarks resource if we find that the Bookmarks.plist file exists. But we don't actually check to see if there are any importable contents from that file.

This bug is to update our migrators so that instead of just lazily returning resources when the files exist, that we do some extra work to detect whether or not there's importable data within those files, and only then return those resources. Yes, that means some additional up-front work, but ultimately, this makes for a better user experience rather than announcing that we imported 0 bookmarks (for this particular case).

Converting this ticket into a meta bug that will contain tickets for each unique migrator