This patch implements the T2T (term-to-type) transformation in patterns.
Patterns that are checked against a visible forall can now be written
without the `type` keyword:

	  \(type t) (x :: t) -> ...   -- old
	  \t (x :: t) -> ...          -- new

The `t` binder is parsed and renamed as a term pattern (Pat), but
then undergoes a conversion to a type pattern (HsTyPat).
See the new function pat_to_type_pat in compiler/GHC/Tc/Gen/Pat.hs