ASN1_STRING_print_ex is extremely complex and attempting to implement
RFC2253, so write some tests for it. Along the way, unexport
CHARTYPE_*, which are internal book-keeping used in
ASN1_STRING_print_ex.
Change-Id: Idb27cd40fb66dc099d1fd6d039a00404608c2063
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/48776
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>