Programmatic sweeps of parameterized DSLX tops

Currently, ir conversion requires the top to be unparameterized. This can make doing parametric sweeps painfully manual or require the use of external template-style hacks.

Ideally, IR conversion would have a mechanism to pre-populate the parametric environment for the top proc. This would require some way to represent DSLX values that a commandline tool can handle (it seems like a proto format for DSLX parametric values would be needed in the general case, e.g. parameters that have aggregate types). Proc state init already has a format, perhaps that would be sufficient (however, I think this is IR level rather than DSLX).

In addition to sweeps, sometimes it's convenient to codegen a library function/proc directly, e.g. `Ram1RW<32, 1024>`, without making a new file or adding to a library. The SRAM flow #861 may need to do something like this as part of lowering passes.