tablecmds: fix bug where index rebuild loses replica identity on partitions

Hi Hackers,

I found this bug while working on a related patch [1].

When ALTER TABLE ... ALTER COLUMN TYPE causes an index rebuild, and that index is used as REPLICA IDENTITY on a partitioned table, the replica
identity marking on partitions can be silently lost after the rebuild.

Below is a simple reproduction:
```
-- create a partitioned table and a parition
create table parent (id int not null, val int not null) partition by range (id);
create table child partition of parent for values from (1) to (100);

-- create an index on parent
create unique index indx_1 on parent(id, val);

-- the index is auto created on child, and both indexes’ indisreplident are false
select c.relname as index_name, c.oid as index_oid, i.indisreplident from pg_class c join pg_index i on c.oid = i.indexrelid where (c.relname = 'indx_1' or c.relname = 'child_id_val_idx’);
    index_name    | index_oid | indisreplident
------------------+-----------+----------------
 indx_1           |     24594 | f
 child_id_val_idx |     24595 | f
(2 rows)

-- as replica identity doesn’t recurse, set it on parent and child individually 
alter table parent replica identity using index indx_1;
alter table child replica identity using index child_id_val_idx;

-- now both indexes are marked as replica identity
select c.relname as index_name, c.oid as index_oid, i.indisreplident from pg_class c join pg_index i on c.oid = i.indexrelid where (c.relname = 'indx_1' or c.relname = ‘child_id_val_idx');
    index_name    | index_oid | indisreplident
------------------+-----------+----------------
 indx_1           |     24594 | t
 child_id_val_idx |     24595 | t
(2 rows)

-- alter a column type, the column is part of the index, it will cause the index to rebuid
alter table parent alter val type bigint;

-- from the OIDs, we can see both indexes are rebuilt, but the child partition loses its replica identity marking
select c.relname as index_name, c.oid as index_oid, i.indisreplident from pg_class c join pg_index i on c.oid = i.indexrelid where (c.relname = 'indx_1' or c.relname = ‘child_id_val_idx');
    index_name    | index_oid | indisreplident
------------------+-----------+----------------
 child_id_val_idx |     24597 | f
 indx_1           |     24596 | t
(2 rows)
```

This patch fixes the bug by tracking replica identity indexes across partition hierarchies and restoring replica identity markings on all affected partitions after index rebuilds.  Regression tests are added.

[1] https://postgr.es/m/CAEoWx2nJ71hy8R614HQr7vQhkBReO9AANPODPg0aSQs74eOdLQ@mail.gmail.com

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/