Extract a RandomPathPlacer prototype from Deep Forest (rP11444) and Schwarzwald (rP15327) duplication, refs #4805, #4804.

This allows creation of paths that are not linear nor sine-shaped like the PathPlacer, refs #892.
To mimic the per-tile path elevation randomization on Deep Forest, use a SmoothElevationPainter and it's randomization argument from rP20354.
Use vector algebra and the mapCenter getter, refs #4845, #4854.