Fix eager aggregation for semi/antijoin inner rels

Fix eager aggregation for semi/antijoin inner rels

Eager aggregation pushes a partial aggregate down to a base or join
relation, to be finalized after that relation is joined with the rest
of the query.  eager_aggregation_possible_for_relation() already
refuses to do this for a relation on the nullable side of an outer
join, but it failed to also refuse it for a relation on the inner side
of a semijoin or antijoin.

Such a join does not emit its inner rows, so a partial aggregate
computed on the inner side does not survive the join and cannot be
combined by the final aggregation.  This can happen only for an
aggregate that references no table column, such as count(*): it is
considered computable on any relation, including the inner one,
whereas an aggregate that references a column is anchored to the outer
side and never reaches the inner relation.

The existing outer-join check did not catch this because it consults
nulling_relids, which only tracks joins that null-extend their inner
side.  Semijoins and antijoins formed from EXISTS, IN, NOT EXISTS, or
NOT IN sublinks do not null-extend and carry no ojrelid, so they are
invisible to that check.

Fix by additionally rejecting any relation that includes inner-side
relations of a semijoin or antijoin but not the join's outer side.
Pushing a partial aggregate to the outer side of such a join, grouped
by the join key, remains valid and is still allowed.

Reported-by: Radim Marek <radim@boringsql.com>
Author: Richard Guo <guofenglinux@gmail.com>
Reviewed-by: Tender Wang <tndrwang@gmail.com>
Discussion: https://postgr.es/m/CAJgoLk+d_P5sKrx-SZt01Acm_j0QnWn6aKJzFJ=waRu_3C8AoQ@mail.gmail.com