Harmonize heapam and tableam parameter names.

Make sure that function declarations use names that exactly match the
corresponding names from function definitions.  Having parameter names
that are reliably consistent in this way will make it easier to reason
about groups of related C functions from the same translation unit as a
module.  It will also make certain refactoring tasks easier.

Like other recent commits that cleaned up function parameter names, this
commit was written with help from clang-tidy.  Later commits will do the
same for other parts of the codebase.

Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/CAH2-WznJt9CMM9KJTMjJh_zbL5hD9oX44qdJ4aqZtjFi-zA3Tg@mail.gmail.com

src/backend/access/transam/multixact.c

@@ -1214,14 +1214,14 @@ GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
  * range, that is, greater to or equal than oldestMultiXactId, and less than
  * nextMXact.  Otherwise, an error is raised.
  *
- * onlyLock must be set to true if caller is certain that the given multi
+ * isLockOnly must be set to true if caller is certain that the given multi
  * is used only to lock tuples; can be false without loss of correctness,
  * but passing a true means we can return quickly without checking for
  * old updates.
  */
 int
 GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members,
-					  bool from_pgupgrade, bool onlyLock)
+					  bool from_pgupgrade, bool isLockOnly)
 {
 	int			pageno;
 	int			prev_pageno;
@@ -1263,7 +1263,7 @@ GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members,
 	 * we can skip checking if the value is older than our oldest visible
 	 * multi.  It cannot possibly still be running.
 	 */
-	if (onlyLock &&
+	if (isLockOnly &&
 		MultiXactIdPrecedes(multi, OldestVisibleMXactId[MyBackendId]))
 	{
 		debug_elog2(DEBUG2, "GetMembers: a locker-only multi is too old");