Add test case for testing LPWStr char width

Author: Exanite

src/Core/Silk.NET.Core.Tests/TestSilkMarshal.cs

@@ -1,4 +1,6 @@
+using System;
 using System.Collections.Generic;
+using System.Runtime.InteropServices;
 using Silk.NET.Core.Native;
 using Xunit;
 
@@ -14,6 +16,32 @@ public class TestSilkMarshal
         NativeStringEncoding.LPUTF8Str,
         NativeStringEncoding.LPWStr,
     };
+
+    [Fact]
+    public unsafe void TestEncodingLPWStr()
+    {
+        var input = "Hello world";
+        
+        // LPWStr is 2 bytes on Windows, 4 bytes elsewhere (usually)
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            var pointer = SilkMarshal.StringToPtr(input, NativeStringEncoding.LPWStr);
+            
+            Assert.Equal(input.Length, (int)SilkMarshal.StringLength(pointer, NativeStringEncoding.LPWStr));
+            
+            // Use short for comparison
+            Assert.Equal(new short[] { 0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64 }, new Span<short>((void*)pointer, input.Length));
+        }
+        else
+        {
+            var pointer = SilkMarshal.StringToPtr(input, NativeStringEncoding.LPWStr);
+            
+            Assert.Equal(input.Length, (int)SilkMarshal.StringLength(pointer, NativeStringEncoding.LPWStr));
+            
+            // Use int for comparison
+            Assert.Equal(new int[] { 0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64 }, new Span<int>((void*)pointer, input.Length));
+        }
+    }
 
     [Fact]
     public void TestEncodingString()