✨ Add Xamarin support (iOS) to C# Wrapper

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Suggestion

Description
Xamarin support was temporarily removed but should still be supported under the .NET Standard implementations.
This may require some specialized building of the package for these particular runtimes and more complicated setup so that a developer can easily utilize the library.

The suggestion is to implement Conditions to implement some of the previous code originally in the previously made iOS and Android projects. This may require using [Build Extras](https://github.com/novotnyllc/MSBuildSdkExtras).

-[iOS specifics](https://github.com/microsoft/electionguard-cpp/blob/0bad662f3c6c32f4f7c257b2826d448930736594/bindings/netstandard/ElectionGuard/ElectionGuard.iOS/ElectionGuard.iOS.csproj#L52)

See

Add iOS binaries into runtimes and project
Update documentation after iOS support
Build test project to demonstrate usage but do not commit within PR.

Helpful Links

https://docs.microsoft.com/en-us/nuget/create-packages/multiple-target-frameworks-project-file
https://docs.microsoft.com/en-us/nuget/create-packages/creating-a-package-msbuild
https://docs.microsoft.com/en-us/dotnet/standard/frameworks
https://github.com/edsnider/latestversionplugin/blob/master/src/Xam.Plugin.LatestVersion.csproj
https://docs.microsoft.com/en-us/nuget/create-packages/supporting-multiple-target-frameworks

### Possible Implementation

_No response_

### Anything else?

_No response_

Bắt đầu bằng cách so sánh các project wrapper .NET Standard hiện tại với ElectionGuard.iOS.csproj trước đây được liên kết trong issue, sau đó xem lại hướng dẫn về MSBuildSdkExtras và NuGet đa target. Xác minh các binary runtime iOS và thiết lập project, cập nhật tài liệu, rồi sử dụng một project test riêng để minh họa cách dùng Xamarin mà không commit project đó.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.