Allow ArgumentsSource to reference methods in other types

[JimmyCushnie]

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!

[timcassell]

Maybe do the same thing for ParamsSource?

[JimmyCushnie]

Makes sense. Pushed!

[timcassell]

Can you also please add or update integration tests?

[JimmyCushnie]

I'm having trouble grokking the tests in this repo. I could use some help. Where would be the appropriate place for the new/modified tests? I can't find any existing tests that involve ArgumentsSource or ParamsSource. The tests for other attributes seem unrelated.

[timcassell]

https://github.com/dotnet/BenchmarkDotNet/blob/93d12c42c0adbc33702cdc42e1fc494d2c919208/tests/BenchmarkDotNet.IntegrationTests/ArgumentsTests.cs
https://github.com/dotnet/BenchmarkDotNet/blob/93d12c42c0adbc33702cdc42e1fc494d2c919208/tests/BenchmarkDotNet.IntegrationTests/ParamsTests.cs

[JimmyCushnie]

Thanks very much. Added two new tests to verify the newly-added behavior. All tests are passing locally.

Edit: and I see they're also passing on the CI, nice

[timcassell]

Thanks @JimmyCushnie!