spice-gtk-session: Fix keyboard focus tracking
spice-gtk-session: Fix keyboard focus tracking

This patch changes the "do we have focus?" tracking, to keeping a counter with
how many widgets have focus. The reason for this is that sometimes multiple
spice-widgets can have focus at the same time, yes really! Sometimes (rarely,
hard to reproduce) the focus in event for one window arrives before the
focus out of the other window.

Signed-off-by: Hans de Goede <9fa1be1a5b5729e4c6b404f34c9ce49ff4882fd8@redhat.com>

fgouget/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,dezelin/spice-gtk,SPICE/spice-gtk,mathslinux/spice-gtk,fgouget/spice-gtk,elmarco/spice-gtk,Fantu/spice-gtk,guodong/spice-gtk,elmarco/spice-gtk,SPICE/spice-gtk,dezelin/spice-gtk,dezelin/spice-gtk,flexVDI/spice-gtk,dezelin/spice-gtk,Fantu/spice-gtk,guodong/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,Fantu/spice-gtk,Fantu/spice-gtk,guodong/spice-gtk,elmarco/spice-gtk,mathslinux/spice-gtk,mathslinux/spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,mathslinux/spice-gtk,elmarco/spice-gtk,SPICE/spice-gtk,flexVDI/spice-gtk,guodong/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk