Skip compiler-generated ctors in records

In externally defined symbols, we need to also check for `[CompilerGenerated]`.

src/Orleans.CodeGenerator/Model/SerializableTypeDescription.cs

@@ -173,7 +173,7 @@ public bool IsEmptyConstructable
                     t = t.BaseType;
                 }
 
-                foreach (var ctor in Type.Constructors)
+                foreach (var ctor in Type.Constructors.Where(x => x.IsImplicitlyDeclared))
                 {
                     if (ctor.Parameters.Length != 0)
                     {