opt_merge: Remove and reinsert init when connecting nets.
opt_merge: Remove and reinsert init when connecting nets.

Mutating the SigMap by adding a new connection will throw off FfInitVals
index.  Work around this by removing the relevant init values from index
whenever we connect nets, then re-add the new init value.

Should fix #2920.

cliffordwolf/yosys,YosysHQ/yosys,cliffordwolf/yosys,antmicro/yosys,cliffordwolf/yosys,YosysHQ/yosys,antmicro/yosys,antmicro/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,antmicro/yosys,cliffordwolf/yosys,antmicro/yosys,cliffordwolf/yosys,antmicro/yosys,antmicro/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,cliffordwolf/yosys,cliffordwolf/yosys,cliffordwolf/yosys,cliffordwolf/yosys,antmicro/yosys