reflect: update to Go 1.22 semantics

The IsZero function was changed slightly in Go 1.22, so we'll need to
update it.

While this could in theory break existing programs that rely on the old
behavior, they'd also break with the imminent Go 1.22 release so I don't
think this is a real problem.

src/reflect/benchmark_test.go

@@ -0,0 +1,10 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package reflect_test
+
+type S struct {
+	i1 int64
+	i2 int64
+}