SQLite, DuckDB: Support aggregate ORDER BY without arguments

[LucaCappelletti94]

SQLite and DuckDB accept an aggregate call whose only content is an ORDER BY clause, such as SELECT count(ORDER BY a) FROM t, but the parser failed with Expected: ), found: BY. SQLite documents ORDER BY inside aggregate calls (https://www.sqlite.org/lang_aggfunc.html#aggorderby) and so does DuckDB (https://duckdb.org/docs/current/sql/functions/aggregates#order-by-clause-in-aggregate-functions). SQLite 3.51.1 and DuckDB 1.4.4 both run count(ORDER BY a) and count(ORDER BY a ASC, b DESC) and both reject count(DISTINCT ORDER BY a). SQLite also accepts count(ALL ORDER BY a).

A new dialect method, supports_aggregate_order_by_with_empty_args, enables the form for SQLite, DuckDB and the generic dialect. DISTINCT still requires an argument. Tests now cover every dialect on both sides of the capability.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.29%. Comparing base (ada8314) to head (f168835).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2660   +/-   ##
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  Coverage   81.28%   81.29%           
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  Files          42       42           
  Lines       33920    33936   +16     
  Branches    33920    33936   +16     
=======================================
+ Hits        27571    27587   +16     
  Misses       2785     2785           
  Partials     3564     3564           

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