automation: support building Python 3 Inno installers The core packaging code now supports building Python 3 installers using PyOxidizer. Let's teach the automation code to invoke it so that we produce both Python 2 and Python 3 based exe installers. When publishing the artifacts, the Python 3 versions are preferred over the Python 2 versions given their higher weight (10 versus 9). This may be a controversial change. But I think making Python 3 the default is warranted, as it is the future. The Python 2 installers are still fully supported and can be installed should issues with Python 3 arise. Differential Revision: https://phab.mercurial-scm.org/D8483