packaging: move Inno Setup core logic into a module Aspects of building the Inno Setup and WIX installers are shared. It will make sense for them to share code. Plus, having code in a reusable library (as opposed to a standalone script) is just a better approach. This commit moves the core logic to build the Inno Setup installer into the hgpackaging package. inno/build.py is now a simple frontend script that calls into a module to do the bulk of the work. As part of this change, I also found a typo in build() where it was referencing "iscc" instead of "iscc_exe." Because "iscc" was in the global scope via the only caller, things just happened to work before. Another benefit of always using functions and not putting global code for __main__ in the same file as library code. Differential Revision: https://phab.mercurial-scm.org/D6087

packaging: move find_vc_runtime_files() into hgpackaging.util In preparation for moving the bulk of the Inno Setup code into hgpackaging. Differential Revision: https://phab.mercurial-scm.org/D6086

packaging: move DOWNLOADS dict to hgpackaging.downloads We'll want to keep state in sync between multiple packaging tools. It makes sense to share a central data structure defining downloads. We also change the function to return the downloads entry so callers don't have to access the global DOWNLOADS in the new location. Differential Revision: https://phab.mercurial-scm.org/D6085