Previously, opt_clean would reconnect all ports (including FF Q ports)
to a "canonical" SigBit chosen by complex rules, but would leave the
init attribute on the old wire. This change applies the same
canonicalization rules to the init attributes, ensuring that init moves
to wherever the Q port moved.
Part of another jab at #2920.
The previous code for rerouting wires when inserting tristate buffers
was overcomplicated and didn't handle all cases correctly (in
particular, only cell connections were rewired — internal connections
were not).
