Reproducible build for macOS/OSX (.dmg)

[SomberNight]

Currently the macOS build is not deterministic/reproducible.

It is the last holdout as the Windows exes, Linux AppImage, the Android APKs, and the source dist are all reproducible.

I suspect this might be more convenient if we managed to cross-compile from Linux to macOS first, and then tackle this.

Around early 2018, @bauerj spent some time on trying to make the macOS build reproducible, without success; the approach tried then did not involve cross-compiling from Linux to OSX, but rather to use a Parallels VM with macOS guest running on macOS host, along with small adaptations to the build script (but still using pyinstaller). IIRC the main issue seemed to be compiling the Python interpreter reproducibly. I think bauerj managed to get reproducibility on the same machine, but not across different machines.

@achow101 also tried for HWI, and got similar results.

Note that it would be okay to not build the python interpreter ourselves but e.g. somehow use the "official" build from python.org. This is already what we do for the Windows binaries.

I tried to look several times over the years, but could never find a python project that managed to build reproducible binaries for macOS.