Add an option to check if a node is a direct parent of the current node
This PR adds ability to check whether the given node is an immediate child of a current node, filtering out indirect children.
Shouldn't break the existing API (added simple boolean with default value)
Possible use case:
func _ready():
get_tree().connect("node_added", self, "_on_node_added")
func _on_node_added(node):
if is_a_parent_of(node, true):
# Only care about instanced scenes disregarding their children