contrib: install PyOxidizer 0.16.0
PyOxidizer now provides MSI installers and pre-built Linux binaries.
So we install that way. This significantly reduces the time to bootstrap
a new machine in automation, as building PyOxidizer from source on a low
core count machine takes several minutes.
This change temporarily breaks the ability of the automated environment
to use the in-repo pyoxidizer.bzl configuration file, as there are
backwards-incompatible changes with the upgrade that need to be
reflected. We'll handle those in subsequent commits.
Differential Revision: https://phab.mercurial-scm.org/D10680