#2748 Allow ArgumentsSource to reference methods in other types

Implements #2744

I added a new constructor for ArgumentsSourceAttribute which takes a custom type. I implemented the logic in BenchmarkConverter so that the custom type can be used. The behavior of the existing constructor is preserved.

I updated the docs to explain the new feature.

I renamed a few internal method parameters for clarity.

This is my first contribution to BenchmarkDotNet. Please let me know if I did anything wrong!