[enhancement] IR conversion should keep proc state names

### What's hard to do? (limit 100 words)

DSLX->IR conversion unconditionally puts state in a tuple named `__state`. After flattening, you get a bunch of mangled state names that can be difficult to reference in simulation or grok when debugging. Prepending underscores also sometimes hides the values from VCD dumps (at least this seems to be what verilator does).

### Current best alternative workaround (limit 100 words)

Accept status quo or manual IR rewriting.

### Your view of the "best case XLS enhancement" (limit 100 words)

Names should flow through from DSLX to IR and ideally not be prepended with underscores.