Swap relallfrozen when swapping relation files

When swapping the physical files of two relations we copy the size
statistics from one relation to the other, but we missed the count of
all-frozen pages that was added in PostgreSQL 18. Swap it too so the
statistics stay correct after the swap.

Author: svenklemm

src/import/heapswap.c

@@ -258,6 +258,14 @@ ts_swap_relation_files(Oid r1, Oid r2, bool target_is_pg_class, bool swap_toast_
 		swap_allvisible = relform1->relallvisible;
 		relform1->relallvisible = relform2->relallvisible;
 		relform2->relallvisible = swap_allvisible;
+
+#if PG18_GE
+		int32 swap_allfrozen;
+
+		swap_allfrozen = relform1->relallfrozen;
+		relform1->relallfrozen = relform2->relallfrozen;
+		relform2->relallfrozen = swap_allfrozen;
+#endif
 	}
 
 	/*