GD-15: Add reset function to mock and spy

[MikeSchulze]

I need a reset for used spy or mock for continus testing without creating a new one

Describe the solution you'd like

func test_reset():
	var instance :Node = auto_free(Node.new())
	var spy_node = spy(instance)
	
	# call with different arguments
	spy_node.set_process(false) # 1 times
	spy_node.set_process(true) # 1 times
	spy_node.set_process(true) # 2 times
	
	verify(spy_node, 2).set_process(true)
	verify(spy_node, 1).set_process(false)
	
	# now reset the spy
	reset(spy_node)
	# verify all counters are rested
	verify_no_interactions(spy_node)

This will help a very lot to test different use cases on one spy or mock objet in a single test

[MikeSchulze]

added beta v0.9.1