gh-113317: Don't use global clinic instance in bad_argument() (#114330)

gh-113317: Don't use global clinic instance in bad_argument() (#114330)

Make it possible for a converter to have multiple includes, by collecting
them in a list on the converter instance. This implies converter includes
are added during template generation, so we have to add them to the
clinic instance at the end of the template generation instead of in the
beginning.