Add shortcut for getting element of array binding

Sources/Adwaita/Model/Extensions/Array.swift

@@ -104,3 +104,20 @@ extension Array {
     }
 
 }
+
+extension Binding where Value == [Any] {
+
+    /// Get a child at a certain index of the array as a binding.
+    /// - Parameters:
+    ///     - index: The child's index.
+    ///     - defaultValue: The value used if the index is out of range does not exist.
+    /// - Returns: The child as a binding.
+    public subscript(safe index: Int?, default defaultValue: Value.Element) -> Binding<Value.Element> {
+        .init {
+            wrappedValue[safe: index] ?? defaultValue
+        } set: { newValue in
+            wrappedValue[safe: index] = newValue
+        }
+    }
+
+}