fix emitSearchGraph, use layout=neato and pos=x,y!

fix emitSearchGraph, use layout=neato and pos=x,y!

Function emitSearchGraph dumps internal state of
orthogonal routing search graph in dot format for debugging.
Output of the function is not used for final user output.

The functions already receives coordinates of nodes.
These coordinates should be used verbatim.

Before this patch `dot` changes locations of search graph nodes and
rendered output image is not useful.

This patch
- adds dummy layout `neato` because attribute `pos` is meaningful
  for only for `neato` and `fdp`.
- adds "!" to force fixed positions by default.

Finally layout engine doesn't changes layout and positions of nodes.

References:
- https://graphviz.org/docs/attrs/pos/
- https://graphviz.org/docs/attr-types/point/