fmt: always handle special methods if print operand is a reflect.Value

fmt: always handle special methods if print operand is a reflect.Value

Check for and call the special printing and format methods such as String
at printing depth 0 when printing the concrete value of a reflect.Value.

Fixes: #16015
Change-Id: I23bd2927255b60924e5558321e98dd4a95e11c4c
Reviewed-on: https://go-review.googlesource.com/30753
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Martin Möhrmann <martisch@uos.de>
TryBot-Result: Gobot Gobot <gobot@golang.org>