WIP: A simple STG tag-inference pass
This MR addresses #16970 by adding a very simple tag-inference pass.
For comparison, we have the more-sophisticated (but more complicated)
To try this pass, use
-dverbose-stg2stg to see what the analysis discovers. In its current incarnation the results of the analysis are immediately discarded, so it has no effect as yet.
What is missing:
- A subsequent pass to add any missing eval's around
StgConAppnodes, guided by the analysis.
- We probably want to export the
TagSigfor top-level binders, and read it in for imported binders.