Fix Example Powerup Collision

[cyypherus]

The collision was previously using the top left corner of the player sprite as the center for collision checks - this updates the example to use the center of the player.

[wick3dr0se]

@cyypherus nice! Last time I ran it, I was thinking about how terrible the collisons were lmao

It's ready for merge right (asking because draft mark)? It looks good to me

[cyypherus]

Not quite, I think I'm still missing something. I'll mark it ready when I get it straightened out.

[cyypherus]

This should be good to go now.
Position now always represents the center of the sprite so the rendering code has been modified a bit.
Power ups now have a width & a height for uniformity & collision uses the size of both the powerup & the player to check collision.