compiler: correctly generate code for local named types

It is possible to create function-local named types:

    func foo() any {
        type named int
        return named(0)
    }

This patch makes sure they don't alias with named types declared at the
package scope.

Bug originally found by Damian Gryski while working on reflect support.

testdata/interface.go

@@ -93,6 +93,12 @@ func main() {
 			a int
 			b int
 		}{3, 6}},
+		{true, named1(), named1()},
+		{true, named2(), named2()},
+		{false, named1(), named2()},
+		{false, named2(), named3()},
+		{true, namedptr1(), namedptr1()},
+		{false, namedptr1(), namedptr2()},
 	}
 	for i, tc := range interfaceEqualTests {
 		if (tc.lhs == tc.rhs) != tc.equal {
@@ -277,3 +283,32 @@ func (f FooByte) Byte() byte { return byte(f) }
 type Byter interface {
 	Byte() uint8
 }
+
+// Make sure that named types inside functions do not alias with any other named
+// functions.
+
+type named int
+
+func named1() any {
+	return named(0)
+}
+
+func named2() any {
+	type named int
+	return named(0)
+}
+
+func named3() any {
+	type named int
+	return named(0)
+}
+
+func namedptr1() interface{} {
+	type Test int
+	return (*Test)(nil)
+}
+
+func namedptr2() interface{} {
+	type Test byte
+	return (*Test)(nil)
+}