apidiff: compare Basic types' kinds for correspondence

When determining if two basic types correspond, just compare their kinds
like the definition of types.Identical does.

Change-Id: I6ed0fda3ca686dcfbd8a1df974b07cf48d11239d
Reviewed-on: https://go-review.googlesource.com/c/exp/+/508495
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

apidiff/correspondence.go

@@ -30,7 +30,9 @@ func (d *differ) corr(old, new types.Type, p *ifacePair) bool {
 	// Structure copied from types.Identical.
 	switch old := old.(type) {
 	case *types.Basic:
-		return types.Identical(old, new)
+		if new, ok := new.(*types.Basic); ok {
+			return old.Kind() == new.Kind()
+		}
 
 	case *types.Array:
 		if new, ok := new.(*types.Array); ok {