Allow validation to be looked up by name

Toolkit.Foundation/ReadOnlyIndexDictionary.cs

@@ -0,0 +1,56 @@
+using System.Collections;
+using System.Diagnostics.CodeAnalysis;
+
+namespace Toolkit.Foundation;
+
+public class ReadOnlyIndexDictionary<TKey, TValue> :
+    IReadOnlyDictionary<TKey, TValue>, 
+    IReadOnlyIndexDictionary<TKey, TValue> 
+    where TKey : notnull
+{
+    private readonly Dictionary<TKey, TValue> dictionary;
+    private readonly List<KeyValuePair<TKey, TValue>> indexedItems;
+
+    public ReadOnlyIndexDictionary(IDictionary<TKey, TValue> items)
+    {
+        dictionary = new Dictionary<TKey, TValue>(items);
+        indexedItems = [.. dictionary];
+    }
+
+    public TValue this[TKey key] =>
+        dictionary[key];
+
+    public KeyValuePair<TKey, TValue> this[int index] =>
+        indexedItems[index];
+
+    public IEnumerable<TKey> Keys =>
+        dictionary.Keys;
+
+    public IEnumerable<TValue> Values =>
+        dictionary.Values;
+
+    public int Count => dictionary.Count;
+
+    public bool ContainsKey(TKey key) =>
+        dictionary.ContainsKey(key);
+
+    public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator() =>
+        dictionary.GetEnumerator();
+
+    IEnumerator IEnumerable.GetEnumerator() => dictionary.GetEnumerator();
+
+    public bool TryGetValue(TKey key, [MaybeNullWhen(false)] out TValue value)
+    {
+        if (dictionary.TryGetValue(key, out TValue? localValue))
+        {
+            if (localValue is not null)
+            {
+                value = localValue;
+                return true;
+            }
+        }
+
+        value = default;
+        return false;
+    }
+}