Replace BackendIds with 0-based ProcNumbers

See the commit 024c521117579a6d356050ad3d78fdc95e44eefa (Replace BackendIds
with 0-based ProcNumbers) in PostgreSQL 17devel.

Thanks to Yuriy Sokolov for the review.

Author: Marina Polyakova

ptrack.h

@@ -47,6 +47,10 @@
 #define nodeOf(ndbck)		(ndbck).node
 #endif
 
+#if PG_VERSION_NUM >= 170000
+#define InvalidBackendId	INVALID_PROC_NUMBER
+#endif
+
 /*
  * Structure identifying block on the disk.
  */