Add Windows Arm64 support

[mayuki]

Fixes #43

[mayuki]

I can confirm that dotnet test completes without problems on Windows on Arm (Surface Pro 9 with 5G).
But, I have not been able to test it on UWP because it did not build well in my Unity & Visual Studio.

@mangolas
Can you confirm that it works in your environment?

[mangolas]

Great that this is now this far! Unfortunately the precompiled dll from this branch did not work on my test Unity project when compiled to UWP Arm64. I'll investigate if I can replace dll with one I have compiled and then try to figure out what could be the problem.

[mangolas]

Hmm, this is bit weird. So I compiled uwp dll by hand from this branch, and replaced precompiled dll and it didn't work. Then I went to my known working setup where I just renamed the dll to yaha_native and changed the name in code... and it worked... so then I renamed the precompiled branch dll to same name... and it worked as well...

So my conclusion is that for some reason the Cysharp.Net.Http.YetAnotherHttpHandler.Native name does not work properly when compiled with IL2CPP to UWP app. But no idea why 🤷‍♂️

[mayuki]

Thanks for the help with the testing!

I was able to set up a Unity UWP project from scratch and run the UWP app on an Arm64 machine.
It seems that the UWP IL2CPP backend does not search for paths containing .dll if the name specified to DllImport contains a dot.

So in the case of [DllImport("yaha_native")], it searches for yaha_native.dll, but in the case of [DllImport("Cysharp.Net.Http.YetAnotherHttpHandler")], it does not search for Cysharp.Net.Http.YetAnotherHttpHandler.dll and throws a DllNotFoundException.

[mayuki]

Added .dll to the library name only for UWP. This seems to work well in my environment.

[mangolas]

Yay, I was now able to get this branch to work directly with my test project! So finally we can use GRPC in all our supported headset, this is so good! Thanks for great lib.