Create and use lenses for ProcessedTerm and Module

[byorgey]

Splitting out an independent refactoring to simplify #1865. There were many places in the code where we were pattern-matching on ProcessedTerm and/or Module, sometimes only to extract a single field, e.g.

ProcessedTerm (Module s _) _ _ <- maybeInitialCode

This was already getting a bit out of hand, and it also meant that any time we wanted to add an extra field to either ProcessedTerm or Module (as I will be doing in #1865), we would have to change every single such place in the code to add an extra wildcard pattern.

This PR is a refactoring to

1. Derive lenses for all the fields of ProcessedTerm and Module, and
2. Prefer extracting named fields via lenses over pattern-matching in most places in the code.

There were a few places in the code where we destructure a ProcessedTerm and use almost all the fields (e.g. when initializing a robot machine); I left those alone, first because extracting all the individual fields would be tedious, but more importantly because if we ever added any new fields in the future, it's likely we would actually want to use them in those contexts as well.