go/types, types2: mention type decl scopes in Info.Scopes documentation

We now may have a scope associated with a type declaration, so need to
update our API documentation accordingly.

Change-Id: Ic66dc3b7cd1969b25fb7c4bee986d76ab3544042
Reviewed-on: https://go-review.googlesource.com/c/go/+/377655
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/compile/internal/types2/api.go

@@ -265,6 +265,7 @@ type Info struct {
 	//
 	//     *syntax.File
 	//     *syntax.FuncType
+	//     *syntax.TypeDecl
 	//     *syntax.BlockStmt
 	//     *syntax.IfStmt
 	//     *syntax.SwitchStmt

src/go/types/api.go

@@ -260,6 +260,7 @@ type Info struct {
 	//
 	//     *ast.File
 	//     *ast.FuncType
+	//     *ast.TypeSpec
 	//     *ast.BlockStmt
 	//     *ast.IfStmt
 	//     *ast.SwitchStmt