rust-bindings/cargo: bump to gtk-rs 0.16

[lucab]

Next iteration of the gtk-rs stack is out, see https://gtk-rs.org/blog/2022/10/18/new-release.html.
This effectively means bumping glib/gio/gobject to 0.16, with newer requirements on C native dependencies:

GLib/GObject/GIO: minimum 2.56, and supports API up to version 2.74

There is also an hard requirement for a minimum Rust toolchain >= 1.63.
Holding this for now. We'd want to give some time for recent toolchains to spread around.
Also, we would like to have cap-std 1.0 available at the time we do this, so that we can do a single semver break for both at the same time. Tracking ticket for cap-std stabilization is bytecodealliance/cap-std#272.