Expose some low level functions and String operators.

test/demo/main.gd

@@ -54,6 +54,15 @@ func _ready():
 	var array: Array[int] = [1, 2, 3]
 	$Example.test_tarray_arg(array)
 
+	prints("String += operator")
+	prints("  test string +=", $Example.test_string_ops())
+
+	prints("WorkerThreadPool")
+	prints("  test worker_thread_pool", $Example.test_workpool_ops())
+
+	prints("PackedArray iterators")
+	prints("  test packed array iterators", $Example.test_vector_ops())
+
 	prints("Properties")
 	prints("  custom position is", $Example.group_subgroup_custom_position)
 	$Example.group_subgroup_custom_position = Vector2(50, 50)