Install .vapi, .deps, .h files for the Vala libraries. Also install the
data files. .deps files have to be manually generated, there's a feature
request for automated generation at
https://github.com/mesonbuild/meson/issues/9756.
Import the gnome module globally.
Install dependencies on Meson CI.
7e7dcedaf ported from GTK3 to GTK4.
It also removed gspell from main/CMakeLists.txt.
I assume that gspell is not needed anymore and we can thus remove the
requirement from the CI and the cmake file as well.
