Make sprite position getters more effecient

[quinton-ashley]

@codingMASTER398 noticed that sprite.x and sprite.y getters are inefficient with sprites that have physics fixtures because every time they're used, p5play recalculates the sprite's position, converting from meters to pixels. Yet, this calculation only needs to be done if sprite.body.getPosition() changes.

Perhaps one day this could be done with Signals:
https://www.youtube.com/watch?v=JvE_xQVIFF0

But it could presently be done by with boolean flags that store whether the sprite's position was changed either by the user or world.step.