pgsql: Refactor init_params() in sequence.c to not use FormData_pg_sequ

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(at)paquier(dot)xyz>
Reviewed-by: Kirill Reshke <reshkekirill(at)gmail(dot)com>
Reviewed-by: Tomas Vondra <tomas(at)vondra(dot)me>
Discussion: https://postgr.es/m/ZWlohtKAs0uVVpZ3@paquier.xyz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ba3d93b2e806a877f26922e0f9e1845d0ef1511b

Modified Files
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src/backend/commands/sequence.c | 81 +++++++++++++++++++++++++----------------
1 file changed, 49 insertions(+), 32 deletions(-)