pgsql: Fail REPACK in presence of !indisready indexes

Fail REPACK in presence of !indisready indexes

Like VACUUM FULL, non-concurrent REPACK would try to rebuild such
indexes, which can sometimes succeed. Concurrent REPACK would however
fail. The inconsistency is not good, so make them both throw an error
quickly to force the user to make a decision on those indexes (most
likely, drop them).

Author: Álvaro Herrera <alvherre(at)kurilemu(dot)de>
Reported-by: Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>
Suggested-by: Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAN4CZFO5A3YE0Dd-bn7eKrB20pECO3=U0wKg1z2rO=DxgWJJHQ@mail.gmail.com

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e14a2354d9f7e44b0ffcaeaf187aa475e3e7d11b

Modified Files
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contrib/test_decoding/expected/repack.out | 16 +++++++
contrib/test_decoding/sql/repack.sql | 8 ++++
src/backend/commands/repack.c | 71 +++++++++++++++++++++++++++++++
3 files changed, 95 insertions(+)