Refactor initial hash lookup in dynahash.c
The same pattern is used three times in dynahash.c to retrieve a bucket
number and a hash bucket from a hash value. This has popped up while
discussing improvements for the type cache, where this piece of
refactoring would become useful.
Note that hash_search_with_hash_value() does not need the bucket number,
just the hash bucket.
Author: Teodor Sigaev
Reviewed-by: Aleksander Alekseev, Michael Paquier
Discussion: https://postgr.es/m/
5812a6e5-68ae-4d84-9d85-
b443176966a1@sigaev.ru