Draw directional arrows without trigonometry

[hexawyz]

📝 Description of the Change

This removes the reliance on trigonometric functions to draw a directional arrow. Trigonometric functions would generally be more expensive than other operations and introduce tiny inaccuracies in results where otherwise avoidable.
Instead, we can use pure vector math to achieve the same result in a more straightforward way.
The only expensive operation remaining after this change is the Normalize operation, which should still be cheaper than the Atan2, Cos and Sin combo used before.
The change should give a few extra FPS in case there are many animated arrows on sceen, but I have not measured this with ultra high precision.
The new code here would also benefit from optimizations if WPF's Vector is improved to support AVX. (Which does not seem to be the case at the moment)

This is the small change I mentioned here: #249

🐛 Possible Drawbacks

• I assume that the length is non-zero, which will hopefully always be the case. More sensible checks can be added in the calling code if this is ever a problem.
• I have not checked if the new code is drawing the arrow in the same order as before (CW or CCW), but I don't think it matters a lot.