Refactor init_params() in sequence.c to not use FormData_pg_sequence_data

Refactor init_params() in sequence.c to not use FormData_pg_sequence_data

init_params() sets up "last_value" and "is_called" for a sequence
relation holdind its metadata, based on the sequence properties in
pg_sequences.  "log_cnt" is the third property that can be updated in
this routine for FormData_pg_sequence_data, tracking when WAL records
should be generated for a sequence after nextval() iterations.  This
routine is called when creating or altering a sequence.

This commit refactors init_params() to not depend anymore on
FormData_pg_sequence_data, removing traces of it in sequence.c, making
easier the manipulation of metadata related to sequences.  The knowledge
about "log_cnt" is replaced with a more general "reset_state" flag, to
let the caller know if the sequence state should be reset.  In the case
of in-core sequences, this relates to WAL logging.  We still need to
depend on FormData_pg_sequence.

Author: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Kirill Reshke <reshkekirill@gmail.com>
Reviewed-by: Tomas Vondra <tomas@vondra.me>
Discussion: https://postgr.es/m/ZWlohtKAs0uVVpZ3@paquier.xyz