Bump to autocxx-bindgen 0.59.5.
Bump to autocxx-bindgen 0.59.5.

Also specify an exact version, since autocxx is only tested when closely
paired with a specific version of autocxx-bindgen. Other semver pairings
may work, but it seems best to insist.

Pre-requisite for #711

google/autocxx,google/autocxx,google/autocxx,google/autocxx