tests: add testcase for abc9 -dff preserving flop names
tests: add testcase for abc9 -dff preserving flop names

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