Improve the Search in-memory evaluator. Implement a custom iterator and reduce allocations.

[fiseni]

The current SearchMemoryEvaluator implementation is as follows.

public IEnumerable<T> Evaluate<T>(IEnumerable<T> query, ISpecification<T> specification)
{
    foreach (var searchGroup in specification.SearchCriterias.GroupBy(x => x.SearchGroup))
    {
      query = query.Where(x => searchGroup.Any(c => c.SelectorFunc(x).Like(c.SearchTerm)));
    }

    return query;
}

This looks relatively simple, but there are a lot of hidden allocations. Moreover, the number of allocations is not constant, and it depends on the size of the input collection.

We need to implement a custom iterator and come up with an allocation-free GroupBy implementation. We may keep the search expressions sorted by search group, and then slice to get the groups.

Breaking Changes:
The SearchEvaluator was renamed to SearchMemoryEvaluator. It was causing unnecessary name collisions with EF plugin evaluators.