Report progress of REINDEX operations

This uses the same infrastructure that the CREATE INDEX progress
reporting uses.  Add a column to pg_stat_progress_create_index to
report the OID of the index being worked on.  This was not necessary
for CREATE INDEX, but it's useful for REINDEX.

Also edit the phase descriptions a bit to be more consistent with the
source code comments.

Discussion: https://www.postgresql.org/message-id/ef6a6757-c36a-9e81-123f-13b19e36b7d7%402ndquadrant.com

src/backend/catalog/index.c

@@ -3286,12 +3286,20 @@ reindex_index(Oid indexId, bool skip_constraint_checks, char persistence,
 	heapId = IndexGetRelation(indexId, false);
 	heapRelation = table_open(heapId, ShareLock);
 
+	pgstat_progress_start_command(PROGRESS_COMMAND_CREATE_INDEX,
+								  heapId);
+	pgstat_progress_update_param(PROGRESS_CREATEIDX_INDEX_OID,
+								 indexId);
+
 	/*
 	 * Open the target index relation and get an exclusive lock on it, to
 	 * ensure that no one else is touching this particular index.
 	 */
 	iRel = index_open(indexId, AccessExclusiveLock);
 
+	pgstat_progress_update_param(PROGRESS_CREATEIDX_ACCESS_METHOD_OID,
+								 iRel->rd_rel->relam);
+
 	/*
 	 * The case of reindexing partitioned tables and indexes is handled
 	 * differently by upper layers, so this case shouldn't arise.
@@ -3442,6 +3450,8 @@ reindex_index(Oid indexId, bool skip_constraint_checks, char persistence,
 				 errdetail_internal("%s",
 									pg_rusage_show(&ru0))));
 
+	pgstat_progress_end_command();
+
 	/* Close rels, but keep locks */
 	index_close(iRel, NoLock);
 	table_close(heapRelation, NoLock);