RE: Plan an inner join as a semijoin under eager deduplication

Hi hackers,

Here is v2:

- 0008 no longer sets aside and restores cached selectivity. It now marks
the pass on PlannerInfo and bypasses the cache while the mark is set.
This covers the per-subclause selectivities an OR clause caches, which
v1 of this series missed.

- EagerAggMode replaces the booleans and empty list checks previously
threaded through the series.

- Deduplication paths are created with AGGSPLIT_SIMPLE, so they are
costed as plain groupings and print without a Partial label. The function
that relabeled them is gone.

- Because the mode is now explicit, 0015 also reaches a plain
deduplication. Two plans lose a repeated grouping.

- 0012 is new. It splits the construction of GroupingExprInfos out of
create_grouping_expr_infos(). This is the only change in patch count.

Thanks,
Will