Re: PoC/WIP: Extended statistics on expressions

This already needs to be rebased on 55dc86eca.

And needs to update rules.out.

And doesn't address this one:

On Sun, Jan 17, 2021 at 10:53:31PM -0600, Justin Pryzby wrote:
> | postgres=# CREATE TABLE t(i int);
> | postgres=# CREATE STATISTICS s2 ON (i+1) ,(i+1+0) FROM t;
> | postgres=# \d t
> |                  Table "public.t"
> |  Column |  Type   | Collation | Nullable | Default 
> | --------+---------+-----------+----------+---------
> |  i      | integer |           |          | 
> | Indexes:
> |     "t_i_idx" btree (i)
> | Statistics objects:
> |     "public"."s2" (ndistinct, dependencies, mcv) ON  FROM t
> 
> on ... what ?

-- 
Justin