pgcrypto: Fix incorrect argument vs PG_GETARG*() mappings

pgcrypto: Fix incorrect argument vs PG_GETARG*() mappings

The following functions use a mix of bytea and text arguments, but their
C internals always used PG_GETARG_BYTEA_PP(), creating an incorrect mix
with the argument types expected by encrypt_internal():
- pgp_sym_encrypt_bytea(bytea,text[,text])
- pgp_sym_encrypt(text,text[,text])
- pgp_sym_decrypt_bytea(bytea,text[,text])
- pgp_sym_decrypt(bytea,text[,text])
- pgp_pub_encrypt_bytea(bytea,bytea[,text])
- pgp_pub_encrypt(text,bytea[,text])
- pgp_pub_decrypt_bytea(bytea, bytea[,text[,text]])
- pgp_pub_decrypt(bytea,bytea[,text[,text]])

This commit fixes the inconsistencies between the PG_GETARG*() macros
and the argument types of each function.

Both BYTEA_PP() and TEXT_PP() rely on PG_DETOAST_DATUM_PACKED(), that
returns an unaligned pointer, so this was not leading to an actual
problem as far as I know, but let's be consistent.

Author: Shihao Zhong
Discussion: https://postgr.es/m/CAGRkXqRfiWT--DzVPx_UGpNHTt0YT5Jo8eV2CtT56jNP=QpXSQ@mail.gmail.com