Set input purpose / hints in the demo, both to show off that this is possible, and perhaps to improve the experience once the Shell learns to make use of this. Currently I can see GTK forwarding it as
zwp_text_input_v3::set_content_type()... and then nothing changes in the OSK.
The last commit adds GTK as a wrap. Given that you're already using subprojects/wraps but not for GTK, you must have some good reason for not doing that. My reasoning for adding it is that Adwaita depends on unstable / newer versions of GTK than even Fedora ships (and my other machine runs Debian Stable...), and this makes it work automatically. But feel free to drop this commit if this is a bad idea for some reason.