[RWRoute] Adjust wire base costs + cross SLR estimates

[eddieh-xlnx]

1. Adjust wire base costs such that:
   i. A NODE_SINGLE/NODE_DOUBLE can (typically) no longer lead to a lower total path cost than the NODE_LOCAL that feeds it, even if it gets us closer to the sink. The reasoning is that we want all the equivalent-cost NODE_LOCAL-s to be explored before allowing single/double wires to be taken, in case there is a chance that a longer wire (double/quad) that can get us there even more efficiently.

Take for example the following, where the sink is solely to its north:

LAG_LAG_X102Y359/RXD1 -> INT_X103Y359/INT_NODE_SDQ_74_INT_OUT0 [C0] -> INT_X103Y359/EE4_W_BEG4
                                                                    -> INT_X103Y359/NN1_W_BEG4  [C1]
                                                                    -> INT_X103Y359/NN2_W_BEG4  [C2]
                                                                    -> INT_X103Y359/WW4_W_BEG4
                      -> INT_X103Y359/INT_NODE_SDQ_74_INT_OUT1 [C0] -> INT_X103Y359/EE2_W_BEG5
                                                                    -> INT_X103Y359/NN1_W_BEG5
                                                                    -> INT_X103Y359/NN4_W_BEG4  [C3]
                                                                    -> INT_X103Y359/WW2_W_BEG5
                      -> INT_X103Y359/INT_NODE_SDQ_76_INT_OUT0 [C0] -> ...
                      -> INT_X103Y359/INT_NODE_SDQ_76_INT_OUT0 [C0] -> ...

Now, expansion of LAG_LAG_X102Y359/RXD1 would place all INT_NODE_SDQ_7[46]_INT_OUT[01] nodes onto the priority queue, all with the same cost of C0.

If NN1 or NN2's cost (C1/C2) was smaller than C0, then RWRoute would explore those nodes ahead of the other INT_NODE_SDQs and miss out on the NN4 (which potentially leads to a NN12)

Ideally, we want: C1 (NN1) > C2 (NN2) > C0 > C3 (NN4) assuming that the sink is at least 4 tiles away such that single and double wires are not explored before all the SDQ nodes are explored, but quads and longs that close the distance to the sink will take priority.

2. Fix distance estimate to sink for cross-SLR connections
3. Do not explore RouteNodeGraph.accessibleWireOnlyIfAboveBelowTarget nodes (e.g. INT_NODE_IMUX/BYPASS/BOUNCE/etc.) nodes if no SLR crossing needed to reach sink

[eddieh-xlnx]

Suggested change

biasCost = 0;