packaging: support building WiX installers with PyOxidizer We initially implemented PyOxidizer support for Inno installers. That did most of the heavy work of integrating PyOxidizer into the packaging system. Implementing WiX installer support was pretty straightforward. Aspects of this patch look very similar to Inno's. The main difference is the handling of the Visual C++ Redistributable Runtime files. The WiX installer was formerly using merge modules to install the VC++ 9.0 runtime because this feature is supported by the WiX installer (it isn't easily available to Inno installers). Our strategy for the runtime files is to install the vcruntime140.dll file next to hg.exe just like any other file. While we could leverage WiX's functionality for invoking a VCRedist installer, I don't want to deal with the complexity at this juncture. So, we let run_pyoxidizer() copy vcruntime140.dll into the staging directory (like it does for Inno) and our dynamic WiX XML generator picks it up as a regular file and installs it. We did, however, have to teach mercurial.wxs how to conditionally use the merge modules. But this was rather straightforward. Comparing the file layout of the WiX installers before and after: * Various lib/*.{pyd, dll} files no longer exist * python27.dll was replaced by python37.dll * vcruntime140.dll was added All these changes are expected due to the transition to Python 3 and to PyOxidizer, which embeded the .pyd and .dll files in hg.exe. Differential Revision: https://phab.mercurial-scm.org/D8477