Use content-only ASN.1 primitives

Use content-only ASN.1 primitives

As part of implicit tag support, rework ASN.1 encoding primitives so
that they encode only content, not tags.  Combine primitives which
become identical with this change.  The new atype_primitive type
invokes a primitive encoder and adds a tag.  atype_fn_len is split
into atype_string and atype_opaque, both of which are hardcoded to
use asn1_encode_bytestring.

For the encoders still using macros, create asn1_addprimitive,
asn1_addinteger, and asn1_addstring macros which call the primitive
encoder function and add a tag.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@25612 dc483132-0cff-0310-8789-dd5450dbe970