Add g_settings_bind_with_mapping_closures()

This is an introspection-friendly version of g_settings_bind_with_mapping(). Having two callbacks that share the same user data is not supported by girepository, so the existing function is not introspectable.

Closes: #564 (closed)

Note, this is marked as a draft because as a new API, it should wait until the GNOME 47 cycle to land. There is a temporary commit incrementing the version so that we generate the correct visibility macros, which should disappear when rebasing next cycle. Despite the draft status, it is ready for review.