Used optimized linear search in more code paths

This commit updates two code paths to use pg_lfind32() introduced by
b6ef167 with TransactionId arrays:
- At the end of TransactionIdIsInProgress(), when checking for the case
of still running but overflowed subxids.
- XidIsConcurrent(), when checking for a serializable conflict.

These cases are less impactful than 37a6e5d, but a bit of
micro-benchmarking of this API shows that linear search speeds up by
~20% depending on the number of items involved (x86_64 and amd64 looked
at here).

Author: Nathan Bossart
Reviewed-by: Richard Guo, Michael Paquier
Discussion: https://postgr.es/m/20220901185153.GA783106@nathanxps13

src/backend/storage/lmgr/predicate.c

@@ -202,6 +202,7 @@
 #include "access/xlog.h"
 #include "miscadmin.h"
 #include "pgstat.h"
+#include "port/pg_lfind.h"
 #include "storage/bufmgr.h"
 #include "storage/predicate.h"
 #include "storage/predicate_internals.h"
@@ -4065,7 +4066,6 @@ static bool
 XidIsConcurrent(TransactionId xid)
 {
 	Snapshot	snap;
-	uint32		i;
 
 	Assert(TransactionIdIsValid(xid));
 	Assert(!TransactionIdEquals(xid, GetTopTransactionIdIfAny()));
@@ -4078,13 +4078,7 @@ XidIsConcurrent(TransactionId xid)
 	if (TransactionIdFollowsOrEquals(xid, snap->xmax))
 		return true;
 
-	for (i = 0; i < snap->xcnt; i++)
-	{
-		if (xid == snap->xip[i])
-			return true;
-	}
-
-	return false;
+	return pg_lfind32(xid, snap->xip, snap->xcnt);
 }
 
 bool