[enhancement] Put module_builder's functions in a shared package

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

Currently, module_builder puts functions in each module. With multi-proc codegen, this means you end up redefining a bunch of functions in many cases.

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

Accept the current behavior- it works.

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

At least for SystemVeriog, it might be nice to pull all these functions outside of their modules and put it in a package instead.