Fix various typos and spelling mistakes in code comments

Author: Justin Pryzby
Discussion: https://postgr.es/m/20220411020336.GB26620@telsasoft.com

src/backend/replication/basebackup_server.c

@@ -195,9 +195,9 @@ bbsink_server_end_archive(bbsink *sink)
 
 	/*
 	 * We intentionally don't use data_sync_elevel here, because the server
-	 * shouldn't PANIC just because we can't guarantee the the backup has been
-	 * written down to disk. Running recovery won't fix anything in this case
-	 * anyway.
+	 * shouldn't PANIC just because we can't guarantee that the backup has
+	 * been written down to disk. Running recovery won't fix anything in this
+	 * case anyway.
 	 */
 	if (FileSync(mysink->file, WAIT_EVENT_BASEBACKUP_SYNC) < 0)
 		ereport(ERROR,

src/backend/replication/logical/reorderbuffer.c

@@ -1876,7 +1876,7 @@ ReorderBufferStreamCommit(ReorderBuffer *rb, ReorderBufferTXN *txn)
  * xid 502 which is not visible to our snapshot.  And when we will try to
  * decode with that catalog tuple, it can lead to a wrong result or a crash.
  * So, it is necessary to detect concurrent aborts to allow streaming of
- * in-progress transactions or decoding of prepared  transactions.
+ * in-progress transactions or decoding of prepared transactions.
  *
  * For detecting the concurrent abort we set CheckXidAlive to the current
  * (sub)transaction's xid for which this change belongs to.  And, during

src/backend/replication/slot.c

@@ -247,7 +247,7 @@ ReplicationSlotValidateName(const char *name, int elevel)
  *     to be enabled only at the slot creation time. If we allow this option
  *     to be changed during decoding then it is quite possible that we skip
  *     prepare first time because this option was not enabled. Now next time
- *     during getting changes, if the two_phase  option is enabled it can skip
+ *     during getting changes, if the two_phase option is enabled it can skip
  *     prepare because by that time start decoding point has been moved. So the
  *     user will only get commit prepared.
  */