No ibus modules for GTK4 with Sway

[Ricardo Wurmus <rekado@elephly.net>]

Hi Guix,

I've reconfigured my system with Sway and I noticed that GTK4
applications now ignore my input method.  GTK3 applications and Emacs
still work fine.

GTK4 applications used to work with IBus under Gnome, so I'm guessing
that some more configuration is required to make this work...  Does
anyone have an idea what might be missing?

FWIW, I find the configuration rather confusing.  Our Cookbook doesn't
contain a working example for using Sway (which is surprising given its
popularity among Guix and Nix users), and whatever the reference manual
mentions when it comes to Sway appears to be unnecessary or overly
complicated (such as the configuration of greetd, which required the
removal of other services).

I still haven't arrived at a comfortable system configuration (GDM still
starts up even though I've removed it from my configuration; only
elogind remains), but the input method problem with GTK4 applications is
the most pressing issue at this time.

I'd be happy for any hints!

-- 
Ricardo