To implement windows-arm64 support, it is needed to add architecture as a subdirectory (https://github.com/flutter/flutter/issues/129805).

In short, when performing a flutter windows build, we have:
- Before: build/windows/runner/Release/gallery.exe
- After: build/windows/x64/runner/Release/gallery.exe

This convention follows what flutter linux build does.

Addresses: https://github.com/flutter/flutter/issues/129805
Addresses: https://github.com/flutter/flutter/issues/116196

Design doc: [flutter.dev/go/windows-arm64](https://flutter.dev/go/windows-arm64)