encoding/xml: use reflect.TypeFor for known types

encoding/xml: use reflect.TypeFor for known types

For #60088

Change-Id: Ib2589b994d304cca1f2e2081639959d80818ac7f
Reviewed-on: https://go-review.googlesource.com/c/go/+/514639
Run-TryBot: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>