Merge 'translate: implement Sequence opcode and fix sort order' from Preston Thorpe

This PR implements the `Sequence` and `SequenceTest` opcodes, although
does not yet add plumbing to emit the latter.
SQLite has two distinct mechanisms that determine the final row order
with aggregates:
Traversal order of GROUP BY, and ORDER BY tiebreaking. When ORDER BY
contains only aggregate expressions and/or constants, SQLite has no
extra tiebreak key, but when ORDER BY mixes aggregate and non-aggregate
terms, SQLite adds an implicit, stable row `sequence` so “ties” respect
the input order.
This PR also fixes an issue with a query like the following:
```sql
SELECT u.first_name, COUNT(*) AS c
FROM users u
JOIN orders o ON o.user_id = u.id
GROUP BY u.first_name
ORDER BY c DESC;
```
Because ORDER BY has only an aggregate (COUNT(*) DESC) and no non-
aggregate terms, SQLite traverses the group key (u.first_name) in DESC
order in this case, so ties on c naturally appear with group keys in
descending order.
Previously tursodb would return the group key sorted in ASC order,
because it was used in all cases as the default

Closes #3287

testing/groupby.test

@@ -326,3 +326,23 @@ sneakers|sneakers|sneakers
 boots|boots|boots
 coat|coat|coat
 accessories|accessories|accessories}
+
+# make sure we return the group by key sorted DESC when the order by has only an aggregate term
+do_execsql_test proper-sort-order {
+	SELECT u.first_name, COUNT(*) AS c
+	FROM users u
+	JOIN products p ON p.id = u.id
+	GROUP BY u.first_name
+	ORDER BY c DESC;
+} {Travis|1
+Tommy|1
+Rachel|1
+Nicholas|1
+Matthew|1
+Jennifer|1
+Jamie|1
+Edward|1
+Daniel|1
+Cindy|1
+Aimee|1}
+