Update aggregateWithConstant() parameters

Problem/Motivation

When trying to add a "Constant Value" field in order to SUM() on a single column, I experienced the following error:

TypeError: Drupal\views_csv_source\Plugin\views\query\ViewsCsvQuery::aggregateWithConstant(): Argument #2 ($records) must be of type League\Csv\MapIterator, array given, called in /code/web/modules/contrib/views_csv_source/src/Plugin/views/query/ViewsCsvQuery.php on line 339 in Drupal\views_csv_source\Plugin\views\query\ViewsCsvQuery->aggregateWithConstant() (line 384 of /code/web/modules/contrib/views_csv_source/src/Plugin/views/query/ViewsCsvQuery.php).

Steps to reproduce

Add a file with a numeric column. Add that column to your view. Add a Constant Value field. Turn on aggregation, group on the Constant Value field and SUM the numeric column. Observe the logs.

Proposed resolution

We should definitely ensure that it accepts an array, as that is what was passed. We can also replace MapIterator with just Iterator, as that's what the execute() function provides.

Remaining tasks

Determine if we can reduce the number of possible types for $records.

User interface changes

API changes

Data model changes