VCD dumping in Chisel 6.5 / svsim

Since Chisel 5, chiseltest (formerly known as chisel-testers2) is no longer supported and has been replaced with svsim in the default chisel-template. Unfortunately, the new system doesn t provide an easy way to dump VCDs from tests. On vanilla Chisel 6.5 this ended up requiring two separate hacks against EphemeralSimulator: Third bonus hack: use the local [ ]