IM sources update results in untimely keymap changes
Apparently, the IM may update its sources untimely (eg. while typing the first character in a password entry). This would result in the KeyboardManager also reloading all keymaps and forgetting about current XKB state. This results in bugs like https://bugzilla.redhat.com/show_bug.cgi?id=1569211 (passwords end up mistyped if the first character requires the shift key).
In order to cut down the worst of this, it seems the KeyboardManager may try to preserve the current keymap through its ID, so we don't spuriously reload the same keymap.