packaging: extract invocation of pyoxidizer to own function I'll be refactoring how the WiX installer creation calls into pyoxidizer and will need a lower level function for facilitating that. The new `run_pyoxidizer()` builds our execution environment (with gettext available) and invokes `pyoxidizer`. Differential Revision: https://phab.mercurial-scm.org/D10687

packaging: rename run_pyoxidizer() I'm going to split this function up in a future commit and I'll want the name "run_pyoxidizer()" for a lower-level function for invoking `pyoxidizer`. Differential Revision: https://phab.mercurial-scm.org/D10686

packaging: move documentation HTML building to own function This is part of some light refactoring to enable us to use PyOxidizer for WiX MSI installer generation. Differential Revision: https://phab.mercurial-scm.org/D10685

pyoxidizer: support code signing Newer versions of PyOxidizer feature built-in support for code signing. You simply declare a code signer in the Starlark configuration file, activate it for automatic signing, and PyOxidizer will add code signatures to signable files as it encounters them. This commit teaches our Starlark configuration file to enable automatic code signing. But only on Windows for the moment, as our immediate goal is to overhaul the Windows packaging. The feature is opt-in: you must pass variables to PyOxidizer's build context via `pyoxidizer build --var` or `pyoxidizer build --var-env` to activate code signing. Differential Revision: https://phab.mercurial-scm.org/D10684