Windows ARM64 builds

[bastimeyer]

Opening this issue here because this question will surely come up soon...

Streamlink's Windows builds rely on pre-built wheels of all the dependencies, including those with Python C-extensions. At the time of writing this, none of Streamlink's dependencies with Python C-extensions provide wheels for Windows on ARM64. Those dependencies are

• lxml (direct dependency)
• pycryptodome (direct dependency)
• brotli (optional dependency)
• cffi (transitive dependency of trio)
• charset-normalizer (transitive dependency of requests)

I'm not going to change the build config here though, because we'd have to build the missing wheels ourselves, so we're stuck and need to wait until all Python dependencies are available as wheels. Manually building dependencies (and their own dependencies) and maintaing alls this is way too much effort.

Building Python itself for ARM64 is pretty straightforward, so there's no issue here. The FFmpeg build-setup still considers the winarm64 build-target experimental, but this will certainly change.

The NSIS installer/uninstaller binaries don't support other archs, so this will be stuck on x86_64. Doesn't matter much though... Switching to a different Windows installer framework like WiX is not worth the effort, as the current setup relies on the pynsist library, which manages the NSIS build script template and file layout.