Apply changes to position, rotation, and scale to the entities'
transformation matrix, taking into account transforms of parents.
An entity will be processed only if it's marked as dirty by another
game.World.Signature[entity] |= Has.Dirty;
sys_transform doesn't depend on the order of entities in the world, but it
works best when parents are added before children. This is the default
insertion order of
instantiate(), but because entities can be later
recycled, it's not guaranteed.
sys_transform also updates the transform's
Parent field. When reparenting
entities, it's not necessary to assign the new parent manually. OTOH, the
Parent field should only be referenced after
sys_transform has already
run during the frame.