TODO: remove items from LaunchServices DB if they are not found on disk

[mszoek]

"Transient" applications like build output or installation images can get into LSDB as they are opened by the user (which is normal behavior). However, if they are removed or the media is unmounted, these entries can prevent LS from correctly opening files handled by that app. We should purge "not found" entries during the app search and try the next match.

[mszoek]

Also register any appURL passed to LSOpenFromURLSpec if the app exists.