pgsql: Make visibilitymap_set() return previous state of vmbits

Make visibilitymap_set() return previous state of vmbits

It can be useful to know the state of a relation page's VM bits before
visibilitymap_set(). visibilitymap_set() has the old value on hand, so
returning it is simple. This commit does not use visibilitymap_set()'s
new return value.

Author: Melanie Plageman
Reviewed-by: Masahiko Sawada, Andres Freund, Nitin Jadhav, Bilal Yavuz
Discussion:
https://postgr.es/m/flat/CAAKRu_ZQe26xdvAqo4weHLR%3DivQ8J4xrSfDDD8uXnh-O-6P6Lg%40mail.gmail.com#6d8d2b4219394f774889509bf3bdc13d,
https://postgr.es/m/ctdjzroezaxmiyah3gwbwm67defsrwj2b5fpfs4ku6msfpxeia%40mwjyqlhwr2wu

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4b565a198b524469df9f3286a6f12778acd9d564

Modified Files
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src/backend/access/heap/visibilitymap.c | 9 +++++++--
src/include/access/visibilitymap.h      | 9 ++++++---
2 files changed, 13 insertions(+), 5 deletions(-)