Add selectivity estimation functions for intarray operators.

Uriy Zhuravlev and Alexander Korotkov, reviewed by Jeff Janes, some cleanup
by me.

contrib/intarray/expected/_int.out

@@ -368,6 +368,7 @@ SELECT '1&(2&(4&(5|!6)))'::query_int;
 
 CREATE TABLE test__int( a int[] );
 \copy test__int from 'data/test__int.data'
+ANALYZE test__int;
 SELECT count(*) from test__int WHERE a && '{23,50}';
  count 
 -------