Add support to native Windows ARM64 with fallback to Win64

[micha102]

Description of Change

Add support to native Windows ARM64 with fallback to Win64.
It allows LibVLCSharp to detect win-arm64 in Core.cs and add fallback to win-x64 folders to preserve compatibility.
It complements mfkl/libvlc-nuget#53 and corresponding PR , which added ARM64 binaries, allowing WPF apps on Windows ARM devices to load LibVLC natively.

Issues Resolved

• fixes issue#586

API Changes

Added:

• internal const string ArchitectureNames.WinArm64 in Constants.cs
• else if (PlatformHelper.IsWindows) { ... } branch in Core.cs to detect Architecture.Arm64
• Fallback search paths for win-x64 when running on win-arm64 in Core.cs

Platforms Affected

• Windows ARM64
• Windows X64 (now including inside branch else if (PlatformHelper.IsWindows) )
• Windows ARM64 (now including inside branch else if (PlatformHelper.IsWindows) )

Behavioral/Visual Changes

None

Before/After Screenshots

Not applicable

Testing Procedure

git clone https://github.com/micha102/libvlcsharp.git
exclude Android, iOS and few others
dotnet pack src/LibVLCSharp/LibVLCSharp.csproj -c Win32Release
dotnet pack src/LibVLCSharp.WPF/LibVLCSharp.WPF.csproj -c Win32Release

PR Checklist

• Rebased on top of the target branch at time of PR
• Changes adhere to coding standard

[micha102]

I added detection of CPU and Bitness for Windows when .NET is greater than 4.0
Well, that defeats the CI pipeline which is presently compiling against net40 as I saw in the last falied CI build.

The thing is if I implement the detection with .NET 4.0, then I need to use Windows specific code.
So, I also need to define a constant matching Windows targeting, otherwise Linux and MacOS builds will complain.

So, in Directory.Build.props, need to add a tag for WINDOWS (there's a WINDOWS_MODERN tag for UWP so that's good)

  <PropertyGroup Condition="'$(Configuration)' == 'Win32Debug'">
    <DefineConstants>$(DefineConstants);WINDOWS;DEBUG</DefineConstants>
  </PropertyGroup>
  <PropertyGroup Condition="'$(Configuration)' == 'Win32Release'">
    <DefineConstants>$(DefineConstants);WINDOWS;RELEASE</DefineConstants>
  </PropertyGroup>

Then, in PlatformHelper.cs, need to add

public static bool IsWindowsArm64
{
#if (WINDOWS || WINDOWS_MODERN) && NET40
    get
    {
        SYSTEM_INFO info;
        GetNativeSystemInfo(out info);
        return info.wProcessorArchitecture == ProcessorArchitecture.Arm64;
    }
#elif (WINDOWS || WINDOWS_MODERN) && !NETSTANDARD1_1
    get => IsWindows && RuntimeInformation.ProcessArchitecture == Architecture.Arm64;
#else
    get => false;
#endif
}

And finally I can do Core.cs a simple

else if (PlatformHelper.IsWindowsArm64)
{
    arch = ArchitectureNames.WinArm64;
}

But since, Windows ARM64 is newly supported, I don't think it's worth it to implement detection for .NET 4.0

Let me know if it's OK, or I must implement it for .NET 4.0 too.