Background

Currently the only Flutter Windows SDK assumes a Windows AMD64 host. This runs on Windows Arm64 hosts using emulation, which affects performance.

Solution

Create and upload a separate Flutter Windows SDK for Windows Arm64 hosts. This may require editing the packaging/packaging recipe, the prepare_package.dart script, and creating new LUCI builders (here and here).

Update the Windows installation docs (here) to allow users to choose the right SDK for their computer's architecture, similar to the macOS docs.

The Flutter SDK archive page loads archives from this JSON file ([here](this script)). This page should automatically show Windows Arm64 SDKs once they exist.

Part of #62597

/cc @pbo-linaro