pgsql: Preserve replica identity index across ALTER TABLE rewrite

Preserve replica identity index across ALTER TABLE rewrite

If an index was explicitly set as replica identity index, this setting
was lost when a table was rewritten by ALTER TABLE. Because this
setting is part of pg_index but actually controlled by ALTER
TABLE (not part of CREATE INDEX, say), we have to do some extra work
to restore it.

Based-on-patch-by: Quan Zongliang <quanzongliang(at)gmail(dot)com>
Reviewed-by: Euler Taveira <euler(dot)taveira(at)2ndquadrant(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/c70fcab2-4866-0d9f-1d01-e75e189db342(at)gmail(dot)com

Branch
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/c9ef507e82ebb2bffc50e531edd6fb4593dd5146

Modified Files
--------------
src/backend/commands/tablecmds.c | 42 +++++++++++++++++++++++
src/backend/utils/cache/lsyscache.c | 23 +++++++++++++
src/include/utils/lsyscache.h | 1 +
src/test/regress/expected/replica_identity.out | 46 ++++++++++++++++++++++++++
src/test/regress/sql/replica_identity.sql | 21 ++++++++++++
5 files changed, 133 insertions(+)