Add Flutter Windows app support

[chenzww]

Cpp(on windows) is to difficult for me. Will it add support for Windows app? Currently, Microsoft officially crate which name windows already support access any Windows API. If possible, I hope it will completely replace cpp with Rust on development windows app.

[shekohex]

I'm sure you can use this project on Windows, by writing your code and build the rust project for windows (producing a .dll shared lib) then you load it as you load any library on Linux or macOS and it should surely work like any other platform.

I've tested it before, for running dart testing over a windows machine when I have access to one last year. (but currently, I don't have access to one, so keep me updated if it does not work.)

[maxnemoy]

confirm it works great for windows

[davehorner]

@maxnemoy would be interested in notes on how it works on windows. I have tried 'flutter create .' and this is what I get from a build.

`# flutter build windows --no-sound-null-safety

Building without sound null safety
For more information see https://dart.dev/null-safety/unsound-null-safety

packages/adder_ffi/lib/adder.dart(5,16): error G311314CC: Method not found: 'add'. [C:\working\flutter\flutterust\build\windows\flutter\flutter_assemble.vcxproj]
packages/scrap_ffi/lib/scrap.dart(31,12): error G311314CC: Method not found: 'error_message_utf8'. [C:\working\flutter\flutterust\build\windows\flutter\flutter_assemble.vcxproj]
C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(247,5): error MSB8066: Custom build for 'C:\working\flutter\flutterust\build\windows\CMakeFiles\ec487d42ab240c697667441dca0168bb\flutter_windows.dll.rule;C:\working\flutter\flutterust\build\windows\CMakeFiles\d018b0b2122db738001a3223cc8ccec7\flutter_assemble.rule;C:\working\flutter\flutterust\windows\flutter\CMakeLists.txt' exited with code 1. [C:\working\flutter\flutterust\build\windows\flutter\flutter_assemble.vcxproj]
Building Windows application...
Build process failed.`

I would be interested in helping to get the windows build working. Gonna take some time to figure out what to do next... if someone has some suggestions lmk.