packaging: extract python exe info to own function This is generic functionality. We'll need it for WIX. As part of the port, we expose the full version and return the data as a dict. Differential Revision: https://phab.mercurial-scm.org/D6090

packaging: don't use temporary directory We were no longer doing anything with it after extracting virtualenv and py2exe to the build directory. Differential Revision: https://phab.mercurial-scm.org/D6089

packaging: extract virtualenv and py2exe to build directory The build directory is essentially a cache. We can extract the virtualenv and py2exe package sources to this directory. Differential Revision: https://phab.mercurial-scm.org/D6088