Refactor lock manager initialization to make it a bit less special

Split the shared and local initialization to separate functions, and
follow the common naming conventions. With this, we no longer create
the LockMethodLocalHash hash table in the postmaster process, which
was always pointless.

Reviewed-by: Andreas Karlsson
Discussion: https://www.postgresql.org/message-id/c09694ff-2453-47e5-b26c-32a16cd75ce6@iki.fi

src/backend/utils/init/postinit.c

@@ -606,6 +606,9 @@ BaseInit(void)
 	 */
 	InitXLogInsert();
 
+	/* Initialize lock manager's local structs */
+	InitLockManagerAccess();
+
 	/*
 	 * Initialize replication slots after pgstat. The exit hook might need to
 	 * drop ephemeral slots, which in turn triggers stats reporting.