We were already using `gir -d` and especially now that our files are
separated across two directories that are relative to the directory
containing Gir.toml this only becomes cumbersome. Besides `gir` lacks
functionality to normalize the path, leading to ie.
gstreamer-gl/egl/sys/../../../gir-files in the version comment as a
result.
These functions have been checked to never return NULL. The overrides
can hopefully be gone again when C contains better annotations and
trust_return_value_nullability is enabled.
