application: Add X-SnapInstanceName
It's the application's original desktop file name, similar to the already supported X-Flatpak-RenamedFrom.
See also disussion in [1].
[1] https://forum.snapcraft.io/t/proposal-allow-snaps-to-specify-their-exact-desktop-file-id/12689
Lets me find a Snap from Plasma’s notifications.
KF5, too?