pgsql: Fix parallel autovacuum workers ignoring track_cost_delay_timing

Fix parallel autovacuum workers ignoring track_cost_delay_timing changes.

Commit 1ff3180ca01 made the leader of a parallel autovacuum propagate
changes to the cost-based delay parameters to its workers, but missed
track_cost_delay_timing. Workers therefore kept the value they had at
launch: turning the parameter on during the vacuum left
pg_stat_progress_vacuum.delay_time counting only the leader's naps,
and turning it off didn't stop workers from adding theirs. Throttling
itself was not affected.

Fix by adding track_cost_delay_timing to PVSharedCostParams. Since a
worker's setting can now change while it runs, we report its residual
delay time at exit whenever any has been accumulated, rather than only
if track_cost_delay_timing is still on.

Backpatch to v19, where parallel autovacuum was introduced.

Reported-by: Sami Imseih <samimseih(dot)pg(at)gmail(dot)com>
Author: Sami Imseih <samimseih(dot)pg(at)gmail(dot)com>
Reviewed-by: Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>
Reviewed-by: Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>
Reviewed-by: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAN12+YJZaALd3zMeKVVRTwcuY5_yDtR_vMPwWc8QNgeYxrn4Zg@mail.gmail.com
Backpatch-through: 19

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/92a734bf5c7ace23131b711025c75aacd8144482

Modified Files
--------------
src/backend/commands/vacuumparallel.c | 13 +++++++++----
.../modules/test_autovacuum/t/001_parallel_autovacuum.pl | 3 ++-
2 files changed, 11 insertions(+), 5 deletions(-)