packaging: integrate signing into run_wix_packaging() Previously, signing was implemented via a separate function which called build_installer() and then called signing functionality. In this model, in order to implement an alternative build mechanism, we would have to invent a new variant to handle signing as well. This commit merges the signing logic into the function invoking wix. If we pass an argument holding metadata about how to sign, we sign hg.exe and the installer. This means all we have to do is pass in signing info and the signing just works. A slight change here is that signing of hg.exe happens in the staging directory as opposed to before the staging directory is populated. I don't think this matters. Differential Revision: https://phab.mercurial-scm.org/D8475