[NativeAOT] Remove dependency of RuntimeType.GUID on generic custom attribute reader (#95212)

Fixes #95184

Author: jkotas

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/NativeFormat/NativeFormatRuntimeNamedTypeInfo.cs

@@ -77,12 +77,11 @@ public sealed override bool IsByRefLike
                     Handle guidStringArgumentHandle = fahEnumerator.Current;
                     if (fahEnumerator.MoveNext())
                         continue;
-                    if (!(guidStringArgumentHandle.ParseConstantValue(_reader) is string guidString))
+                    if (guidStringArgumentHandle.HandleType != HandleType.ConstantStringValue)
                         continue;
-                    return new Guid(guidString);
+                    return new Guid(guidStringArgumentHandle.ToConstantStringValueHandle(_reader).GetString(_reader));
                 }
             }
-
             return null;
         }