Support three step simulation with VCS

[DavisLiu1989]

To avoid compile library(such as VIVADO primitive libraries) every time, I hope cocotb-test can use three step sim with VCS.
Maybe some function in https://github.com/SpinalHDL/SpinalHDL/blob/dev/sim/src/main/scala/spinal/sim/VCSBackend.scala can as references.
Thanks

[themperek]

I have no access to VCS anymore. Someone would need to do this who has.