Return an error when multiple rows are returned from a scalar subquery

[Mytherin]

Implements #11521
Implements #13469

This PR modifies the behavior of scalar subqueries so that an error is thrown when multiple rows are returned, instead of returning a random row. This aligns the behavior of the system with that of Postgres, instead of that of SQLite.

For example:

select (select unnest(range(10)));
-- Invalid Input Error: More than one row returned by a subquery used as an expression - scalar subqueries can only return a single row.

The old behavior is available through the scalar_subquery_error_on_multiple_rows configuration setting:

SET scalar_subquery_error_on_multiple_rows=false;
D select (select unnest(range(10))) as result;
┌────────┐
│ result │
│ int64  │
├────────┤
│      0 │
└────────┘