add trimming attribute to custom vertex with feature id

tests/SharpGLTF.Cesium.Tests/VertexWithFeatureId.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Numerics;
 
 using SharpGLTF.Geometry.VertexTypes;
@@ -7,6 +8,10 @@ using SharpGLTF.Schema2;
 
 namespace SharpGLTF
 {
+
+    #if NET6_0_OR_GREATER
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields)]
+    #endif
     [System.Diagnostics.DebuggerDisplay("𝐂:{Color} 𝐔𝐕:{TexCoord}")]
     public struct VertexWithFeatureId : IVertexCustom
     {