Use custom collector to avoid intermediate array allocations

[mgravell]

Context #2166

List<T> uses initial-size plus doubling, which means that for large result sets you can get multiple arrays, for example for 90 rows you might have arrays with sizes 16, 32, 64, and 128 for 90, with the final result list using the oversized 128-element array, with 90 elements.

This change uses a custom collector for this part - same logic, but it uses the array-pool so that those intermediate arrays are recycled, and the final array is right-sized, i.e. a list with count 90 and capacity 90, and all intermediate arrays reused.