Imwayland: a straight bugfix + make input method aware of selections (as per text-input-unstable-v3 wayland protocol)

@dorota.czaplejewicz since you're familiar with both ends of this, would you care to have a look?

@adrien.plazas @guido.gunther The pipeline for these will never pass, but the changes are fine (perfect, but you're not supposed to say that).

These changes should ideally be upstreamed, but I'm not the right person to curate bugs for yet another upstream. Also, if you plan to make a flatpak runtime for the librem5, having this (or something along these lines) would be helpful.