Guest sees multiple caps_lock events when caps_lock is remapped to ctrl on the client

Originally reported against virt-viewer

https://gitlab.com/virt-viewer/virt-viewer/-/issues/29

Running on Fedora 33, with GNOME desktop, launch gnome-tweaks

Under additional keyboard options, Caps lock behaviour, select Caps lock is also ctrl.

Now attempt to interact with a guest, pressing Caps lock.

Since SPICE is forwarding raw scancodes, the guest is still going to see a "Caps lock" scancode of course.

The wierd part is that a press+release on the client results in press+release, then a short delay, then press+release in the guest.

It looks like the remapping of capslock to be a modifier in the client is confusing spice-gtk somewhere, causing it to inject an extra set of input events.