go/types, types2: underIs must consider Alias types

Fixes regression from Go 1.22.

For #67547.

Change-Id: I012681c7b8b01b02018b313dd3804690bc7aeed1
Reviewed-on: https://go-review.googlesource.com/c/go/+/587158
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: griesemer

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

@@ -131,6 +131,7 @@ var op2str2 = [...]string{
 // If typ is a type parameter, underIs returns the result of typ.underIs(f).
 // Otherwise, underIs returns the result of f(under(typ)).
 func underIs(typ Type, f func(Type) bool) bool {
+	typ = Unalias(typ)
 	if tpar, _ := typ.(*TypeParam); tpar != nil {
 		return tpar.underIs(f)
 	}

src/go/types/expr.go

@@ -117,6 +117,7 @@ var op2str2 = [...]string{
 // If typ is a type parameter, underIs returns the result of typ.underIs(f).
 // Otherwise, underIs returns the result of f(under(typ)).
 func underIs(typ Type, f func(Type) bool) bool {
+	typ = Unalias(typ)
 	if tpar, _ := typ.(*TypeParam); tpar != nil {
 		return tpar.underIs(f)
 	}

src/internal/types/testdata/fixedbugs/issue67547.go

@@ -20,3 +20,9 @@ func _[P string]() {
 	var s A
 	copy(t, s) // don't report an error for s
 }
+
+func _[P map[int]int]() {
+	type A = P
+	var m A
+	clear(m) // don't report an error for m
+}