packaging: write out editor.rc in Python Let's dynamically generate the file from Python instead of relying on Inno functionality, as that will give more visibility into what's going on. I spotted this as part of converging the install layout of Inno and WiX: the former doesn't install an editor.rc and instead defines the editor via its mercurial.rc file. We will change the behavior of WiX later once it is consuming the staged install directory for packaging. Differential Revision: https://phab.mercurial-scm.org/D7171