Add autocompletion for AnimatedSprite.play()

[timothyqiu]

Implements part of godotengine/godot-proposals#4463. I'm not sure if it's possible to add completion for the animation property.

I only tested this on 3.x because autocompletion on master has been kind of broken for me for a long time.

[Mickeon]

My eyes lit up when I saw this one, thank you!

Regarding the animation property, I could open a more general proposal about autocompleting properties when comparing or assigning, since I don't personally recall anything like that even existing in the Editor currently. It would be logic that plenty of properties would benefit from, not just animation.

[akien-mga]

Thanks!