[php] add array access to NativeStructArray (closes #8893)

std/php/NativeStructArray.hx

@@ -38,4 +38,12 @@ abstract NativeStructArray<T:{}>(NativeArray) to NativeArray {
 	inline function __toObject():T {
 		return Boot.createAnon(this);
 	}
+
+	@:arrayAccess
+	inline function get<V>(key:String):V
+		return this[key];
+
+	@:arrayAccess
+	inline function set<V>(key:String, val:V):V
+		return this[key] = val;
 }