macOS arm64 builds (Apple M1, etc.)

[bastimeyer]

NW.js now provides arm64 builds for macOS since its 0.77.0 release.
https://nwjs.io/blog/v0.77.0/

I'll have a look at this after the next release of Streamlink Twitch GUI.

This doesn't just require new build configs, but also probably a migration of the nw-builder dev-dependency. I've been using my private fork of nw-builder ever since the project got abandoned by its maintainer several years ago. Even though I was involved a bit in its development during the early days of Streamlink Twitch GUI, I never wanted to continue extending nw-builder and I just did a bit of fixing to keep it working for our own purposes here. nw-builder however has been forked and re-built by a new active maintainer, under the same package name on npmjs. I will have to see what's changed and what a potential migration would require in terms of build config and build logic here. They will surely add support for macOS arm64 if they haven't already. It's also possible that my private fork already supports it. I haven't tested this yet, but I also don't really want to continue using it when I already have to rewrite parts of the build config.

The next issue is testing and validating the arm64 builds. I don't have the hardware for that and I'm not sure if emulating via qemu is possible. If it is, then it'll be painfully slow.