Font fallbacks.

Voile/Source/Resources/Resource.cs

@@ -52,6 +52,28 @@ namespace Voile
         {
             Guid = guid;
         }
+
+        public override bool Equals(object? obj)
+        {
+            return obj is ResourceRef<T> other && Guid.Equals(other.Guid);
+        }
+
+        public override int GetHashCode()
+        {
+            return Guid.GetHashCode();
+        }
+
+        public static bool operator ==(ResourceRef<T>? left, ResourceRef<T>? right)
+        {
+            if (ReferenceEquals(left, right)) return true;
+            if (left is null || right is null) return false;
+            return left.Guid == right.Guid;
+        }
+
+        public static bool operator !=(ResourceRef<T>? left, ResourceRef<T>? right)
+        {
+            return !(left == right);
+        }
     }
 
     /// <summary>