Make error messages about WAL segment size more consistent

Make error messages about WAL segment size more consistent

Make the primary messages more compact and make the detail messages
uniform.  In initdb.c and pg_resetwal.c, use the newish
option_parse_int() to simplify some of the option parsing.  For the
backend GUC wal_segment_size, add a GUC check hook to do the
verification instead of coding it in bootstrap.c.  This might be
overkill, but that way the check is in the right place and it becomes
more self-documenting.

In passing, make pg_controldata use the logging API for warning
messages.

Reviewed-by: Aleksander Alekseev <aleksander@timescale.com>
Discussion: https://www.postgresql.org/message-id/flat/9939aa8a-d7be-da2c-7715-0a0b5535a1f7@eisentraut.org