Refactor query cancellation code into src/fe_utils/

Originally, this code was duplicated in src/bin/psql/ and
src/bin/scripts/, but it can be useful for other frontend applications,
like pgbench.  This refactoring offers the possibility to setup a custom
callback which would get called in the signal handler for SIGINT or when
the interruption console events happen on Windows.

Author: Fabien Coelho, with contributions from Michael Paquier
Reviewed-by: Álvaro Herrera, Ibrar Ahmed
Discussion: https://postgr.es/m/alpine.DEB.2.21.1910311939430.27369@lancre

src/bin/scripts/clusterdb.c

@@ -133,7 +133,7 @@ main(int argc, char *argv[])
 		exit(1);
 	}
 
-	setup_cancel_handler();
+	setup_cancel_handler(NULL);
 
 	if (alldb)
 	{