pgsql: Rationalize handling of VacuumParams

Rationalize handling of VacuumParams

This commit refactors the vacuum routines that rely on VacuumParams,
adding const markers where necessary to force a new policy in the code.
This structure should not use a pointer as it may be used across
multiple relations, and its contents should never be updated.
vacuum_rel() stands as an exception as it touches the "index_cleanup"
and "truncate" options.

VacuumParams has been introduced in 0d831389749a, and 661643dedad9 has
fixed a bug impacting VACUUM operating on multiple relations. The
changes done in tableam.h break ABI compatibility, so this commit can
only happen on HEAD.

Author: Shihao Zhong <zhong950419(at)gmail(dot)com>
Co-authored-by: Michael Paquier <michael(at)paquier(dot)xyz>
Reviewed-by: Nathan Bossart <nathandbossart(at)gmail(dot)com>
Reviewed-by: Junwang Zhao <zhjwpku(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAGRkXqTo+aK=GTy5pSc-9cy8H2F2TJvcrZ-zXEiNJj93np1UUw@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/2252fcd4276cfeabae8786ab7c5a421dd674743e

Modified Files
--------------
src/backend/access/heap/vacuumlazy.c | 44 ++++++-------
src/backend/commands/analyze.c | 26 ++++----
src/backend/commands/cluster.c | 2 +-
src/backend/commands/vacuum.c | 118 ++++++++++++++++-------------------
src/backend/postmaster/autovacuum.c | 2 +-
src/include/access/heapam.h | 4 +-
src/include/access/tableam.h | 6 +-
src/include/commands/vacuum.h | 6 +-
8 files changed, 98 insertions(+), 110 deletions(-)