[#26879] YSQL: Fix PG segfault during rewrite on tables with vector indexes

Summary:
The segfault happens because a null pointer is passed for the opclassOids argument to YBCCreateIndex, and subsequently to ybhnswbindcolumnschema. This issue was introduced in commit f8950ff.
Fix the segfault by properly constructing and passing the operator class oids.

Specific code changes:
- pg_yb_utils.c: retrieve the operator class oids from the sys cache (pg_index.indclass) in YbIndexSetNewRelfileNode, and pass it to YBCCreateIndex
- ybvectorwrite.c: use YbGetRelfileNodeId(index) instead of the index's oid in ybvectorcopartitionedbuild.

Jira: DB-16293

Test Plan:
Note: rewrites on tables with vector indexes are still flaky (occasionally cause a tserver FATAL at a later stage) due to a different issue, so this revision doesn't add any automated tests.

Manual test:
```
yugabyte=# CREATE EXTENSION vector;
CREATE EXTENSION
yugabyte=# CREATE TABLE IF NOT EXISTS ybarticles (id int, content_vector vector(1536));
CREATE TABLE
yugabyte=# CREATE INDEX ON ybarticles USING ybhnsw (content_vector vector_l2_ops);
CREATE INDEX
yugabyte=# TRUNCATE TABLE ybarticles;
TRUNCATE TABLE
yugabyte=# SELECT * FROM ybarticles;
 id | content_vector
----+----------------
(0 rows)
```

Reviewers: myang, sergei

Reviewed By: myang

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D44458

Author: fizaaluthra

src/postgres/src/backend/utils/misc/pg_yb_utils.c

@@ -7122,10 +7122,13 @@ YbIndexSetNewRelfileNode(Relation indexRel, Oid newRelfileNodeId,
 						 bool yb_copy_split_options)
 {
 	bool		isNull;
+	HeapTuple   indexTuple;
 	HeapTuple	tuple;
 	Datum		reloptions = (Datum) 0;
 	Relation	indexedRel;
 	IndexInfo  *indexInfo;
+	oidvector  *indclass = NULL;
+	Datum       indclassDatum;
 
 	tuple = SearchSysCache1(RELOID,
 							ObjectIdGetDatum(RelationGetRelid(indexRel)));
@@ -7142,6 +7145,19 @@ YbIndexSetNewRelfileNode(Relation indexRel, Oid newRelfileNodeId,
 	indexInfo = BuildIndexInfo(indexRel);
 
 	YbGetTableProperties(indexRel);
+
+	indexTuple = SearchSysCache1(INDEXRELID,
+								 ObjectIdGetDatum(RelationGetRelid(indexRel)));
+	if (!HeapTupleIsValid(indexTuple))
+		elog(ERROR, "cache lookup failed for index %u",
+			 RelationGetRelid(indexRel));
+
+	indclassDatum = SysCacheGetAttr(INDEXRELID, indexTuple,
+									Anum_pg_index_indclass, &isNull);
+	if (!isNull)
+		indclass = (oidvector *) DatumGetPointer(indclassDatum);
+	ReleaseSysCache(indexTuple);
+
 	YBCCreateIndex(RelationGetRelationName(indexRel),
 				   indexInfo,
 				   RelationGetDescr(indexRel),
@@ -7157,7 +7173,7 @@ YbIndexSetNewRelfileNode(Relation indexRel, Oid newRelfileNodeId,
 				   indexRel->rd_rel->reltablespace,
 				   newRelfileNodeId,
 				   YbGetRelfileNodeId(indexRel),
-				   NULL /* opclassOids */ );
+				   indclass ? indclass->values : NULL);
 
 	table_close(indexedRel, ShareLock);
 

src/postgres/third-party-extensions/pgvector/src/ybvector/ybvectorwrite.c

@@ -457,7 +457,7 @@ IndexBuildResult *
 ybvectorcopartitionedbuild(Relation heap, Relation index, struct IndexInfo *indexInfo)
 {
 	HandleYBStatus(YBCPgWaitVectorIndexReady(
-		YBCGetDatabaseOid(index), index->rd_id));
+		YBCGetDatabaseOid(index), YbGetRelfileNodeId(index)));
 
 	IndexBuildResult *result = palloc0(sizeof(IndexBuildResult));