Separate internal state from TouchLocation 

SizeOf TouchLocation is now 36bytes from 72bytes.
Reducing the size of TouchLocation has been discussed here
mono#2963
That is an explicit conversion operation.
https://github.com/nkast/MonoGame/blob/LightweightTouchLocation/MonoGame.Framework/Input/Touch/InternalTouchLocation.cs#L253

If it's not clear I can re-wright it as `.ToTouchLocation()` or something.