reduce sugar in confusing error messages

This addresses the case where you'd see an error of:

Ambiguous elaboration at:
	r <- pure []
Possible correct results:
	[]
	[]
	[]
By changing it to:

Possible correct results:
	Main.Nil
	PrimIO.Nil
	Prelude.Nil

src/Idris/Resugar.idr

@@ -155,7 +155,9 @@ mutual
   toPTerm : {auto c : Ref Ctxt Defs} ->
             {auto s : Ref Syn SyntaxInfo} ->
             (prec : Nat) -> RawImp -> Core PTerm
-  toPTerm p (IVar fc nm) = toPRef fc nm
+  toPTerm p (IVar fc nm) = if fullNamespace !(getPPrint)
+                             then pure $ PRef fc nm
+                             else toPRef fc nm
   toPTerm p (IPi fc rig Implicit n arg ret)
       = do imp <- showImplicits
            if imp

tests/idris2/with003/expected

@@ -64,9 +64,9 @@ Main> (interactive):1:4--1:6:Ambiguous elaboration at:
 1	:t []
 	   ^^
 Possible correct results:
-	[]
-	[]
-	[]
+	PrimIO.Nil
+	Prelude.Nil
+	Data.Vect.Nil
 Main> [] : Vect 0 ?elem
 Main> [] : List ?a
 Main> (interactive):1:34--1:41:When unifying Vect 0 ?elem and List ?a