Clean up confusing rr-node lookup convention for x/y location of wires.

[vaughnbetz]

The code at https://github.com/verilog-to-routing/vtr-verilog-to-routing/blob/50901246919105b42a534cb58e622cada82be1bf/vpr/src/route/rr_graph2.cpp#L1225C79-L1225C90 swaps the x and y coordinates of CHANX wires when putting them in the rr_node_lookup data structure, and the find function similarly swaps them. This is baffling.

Proposed Behaviour

We should just put them in the lookup with their proper x,y values and the lookup function shouldn't swap them either.

Current Behaviour

It works, but the convention is bizarre, making the code less readable.