packaging: add -python2 to Windows installer filenames We just taught the Windows installers to produce Python 3 variants built with PyOxidizer. Our plan is to publish both Python 2 and Python 3 versions of the installers for Mercurial 5.4. This commit teaches the Inno and WiX installers to add an optional string suffix to the installer name. On Python 2, that suffix is "-python2." We reserve the existing name for the Python 3 installers, which we want to make the default. Differential Revision: https://phab.mercurial-scm.org/D8479