More precise LANGUAGE pragma when forall is used

In all cases when a user attempts to use the forall keyword, GHC suggests enabling RankNTypes. This seems suboptimal, since a more direct way to enable just the syntax is ExplicitForAll. So maybe we should just suggest that instead.

In some cases, the user will immediately thereafter have to add RankNTypes, or Rank2Types, or ExistentialQuantification, etc. So it would be more user friendly to suggest the appropriate extension directly. I don't know how much harder this would be to do.

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 3

added Tbug Trac import typechecker labels

added Plow label

#24448 (closed).

this has the additional ask of immediately suggesting the right extension which I think is a lot more difficult to do, but for this reason I will not close as duplicate