Added partial class for field for validation purposes

Author: szv

src/Codebreaker.ViewModels/Models/Field.Validation.cs

@@ -0,0 +1,8 @@
+namespace Codebreaker.ViewModels.Models;
+
+public partial class Field
+{
+    public bool IsSet =>
+        PossibleColors is null || Color is not null &&
+        PossibleShapes is null || Shape is not null;
+}