Tidy up partial-sig quantification
There's a messy bit of tcSimplifyInfer which concerns how quantify when partial type signatures are involved. This patch tidies it up a lot. Notice that decideQuantification and quantify_tvs get much simpler. And previously the inferred type of a function could be cluttered with phantom variables that were relevant only to the error messgas. See Note [Quantification and partial signatures].
Showing with 57 additions and 58 deletions