[repl] Be able to drive parametric instantiations e.g. for IR/verilog generation

A feature that would be helpful is if we could drive parametric instantiations from the REPL. e.g. consider clz in the stdlib -- it's parametric so only gets generated on demand, but we may want to observe what Verilog gets generated for it stand-alone. It would be nice if we could say something like: `:verilog clz` or similar to cause IR to be generated and subsequently Verilog to be produced.