pgsql: Fix waits of REINDEX CONCURRENTLY for indexes with predicates or

Fix waits of REINDEX CONCURRENTLY for indexes with predicates or expressions

As introduced by f9900df5f94, a REINDEX CONCURRENTLY job done for an
index with predicates or expressions would set PROC_IN_SAFE_IC in its
MyProc->statusFlags, causing it to be ignored by other concurrent
operations.

Such concurrent index rebuilds should never be ignored, as a predicate
or an expression could call a user-defined function that accesses a
different table than the table where the index is rebuilt.

A test that uses injection points is added, backpatched down to 17.
Michail has proposed a different test, but I have added something
simpler with more coverage.

Oversight in f9900df5f949.

Author: Michail Nikolaev
Discussion: https://postgr.es/m/CANtu0oj9A3kZVduFTG0vrmGnKB+DCHgEpzOp0qAyOgmks84j0w@mail.gmail.com
Backpatch-through: 14

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/5bbdfa8a18dc56d3e64aa723a68e02e897cb5ec3

Modified Files
--------------
src/backend/commands/indexcmds.c                   | 13 +++++-
src/test/modules/injection_points/Makefile         |  2 +-
.../injection_points/expected/reindex_conc.out     | 51 ++++++++++++++++++++++
src/test/modules/injection_points/meson.build      |  1 +
.../modules/injection_points/sql/reindex_conc.sql  | 28 ++++++++++++
5 files changed, 92 insertions(+), 3 deletions(-)