Fix the instantiation of data constructors in the GHCi debugger
This bug caused Trac #7386, because in the (rather tricky) "type inference" (aka run time type reconstruction) done by the GHCi debugger, we were failing to instantiate a data type family correctly. When that code was written we didn't *have* data families. I wrote Note [Constructor arg types] to explain the new scheme.
Showing with 34 additions and 5 deletions