compute: type scaffolding for match/replace operations

Created by: rvantonder

This PR introduces types for replace operations we'll support on the compute endpoint down the line. These new type definitions induce a change in RegexpFromQuery, which is broken up into smaller functions now, because the "match regexp groups" will become only a part of a broader set of functions we'll mint going forward.

This is sort-of-but-not-really-experimental "cool new stuff" I've had in mind for a while, so Camden, Keegan and Coury are probably best to review given the context. But Camden's not here so he is missing out on the fun.

Edit: Rok is also a good fit and can get context from reviewing, because things may grow to incorporate LSIF.

Related #26198 (closed)