There are, unfortunately, intermediate CA ceritificates in circulation
that contain the invalid character '&' in some PrintableString fields,
notably Organization Name. This patch allows for ampersand
to be parsed as though it is valid in an ASN.1 PrintableString.

Fixes #22970

Change-Id: Ifab1a10bbff1cdac68e843c6b857ff1a031051aa
Reviewed-on: https://go-review.googlesource.com/81635Reviewed-by: Adam Langley <agl@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>