introduce ty::Value

Co-authored-by: FedericoBruzzone <federico.bruzzone.i@gmail.com>

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -962,7 +962,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                             return Ok(EvaluatedToAmbig);
                         }
                         ty::ConstKind::Error(_) => return Ok(EvaluatedToOk),
-                        ty::ConstKind::Value(ty, _) => ty,
+                        ty::ConstKind::Value(cv) => cv.ty,
                         ty::ConstKind::Unevaluated(uv) => {
                             self.tcx().type_of(uv.def).instantiate(self.tcx(), uv.args)
                         }