Added indexer for immutable sequence

WabiSabi/Collections/ImmutableValueSequence.cs

@@ -8,7 +8,7 @@ namespace WabiSabi.Collections;
 /// it can be compared with other sequences and the equality of two sequences is based on the
 /// equality of the elements.
 /// </summary>
-public readonly struct ImmutableValueSequence<T> : IReadOnlyCollection<T>, IEquatable<ImmutableValueSequence<T>> where T : IEquatable<T>
+public readonly struct ImmutableValueSequence<T> : IReadOnlyList<T>, IEquatable<ImmutableValueSequence<T>> where T : IEquatable<T>
 {
 	private readonly ImmutableArray<T> _elements;
 
@@ -19,6 +19,8 @@ public ImmutableValueSequence(IEnumerable<T> sequence)
 
 	public static ImmutableValueSequence<T> Empty { get; } = new();
 
+	public T this[int index] => _elements[index];
+
 	public int Count => _elements.Length;
 
 	public ImmutableArray<T>.Enumerator GetEnumerator() => _elements.GetEnumerator();