Add in ValuePair::Term

This adds in an enum when matching on positions which can either be types or consts.
It will default to emitting old special cased error messages for types.

compiler/rustc_infer/src/infer/mod.rs

@@ -371,6 +371,7 @@ pub enum ValuePairs<'tcx> {
     Types(ExpectedFound<Ty<'tcx>>),
     Regions(ExpectedFound<ty::Region<'tcx>>),
     Consts(ExpectedFound<&'tcx ty::Const<'tcx>>),
+    Terms(ExpectedFound<ty::Term<'tcx>>),
     TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
     PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
 }