[Feature] Extend the update_as_oneway_platform function to allow normal setting too.

[Ughuuu]

Right now, you are unable to set the normal of the update_as_oneway_platform function. For platforms that are rotated or where you want one way to be in a different direction, this is useful.
Also, it only works with first object being one way platform, not second one (in an intersection). In case the first object is player and second one is platform, the function needs some change to be used.

Also moved the cosinus computation outside of the function, in case someone doesn't wanna use angle but dot product directly (if they already know the value of cosine for that vector)