[WIP] GenAPI: a work around for a generation an explicit interface implementation indexer.

[andriipatsula]

This is a work around solution for the #31570 issue to unblock the A&D team.

Indexer properties is not resolved correctly for the scenario like:

public interface IFooList<T>
{
    T this[int index] { get; set; }
}

public struct Bar<T> : IFooList<T>
{
    // indexer №1
    public T this[int index] { get; set; }

    // indexer №2
    T IFooList<T>.this[int index] { get; set; }
}

Indexer №1 is generated correctly, but explicit interface implementation indexer (№2) is not. I double checked that the customer passes correct reference assemblies, and it seems, it could be a bug in the Roslyn API.

@ericstj could you please review this work around. Once @ViktorHofer returns from his vacation, I will communicate the problem with him.

[ericstj]

This is a work around solution for the #31570 issue to unblock the A&D team.

Unblocking can always happen with a partial file definition, right?

Do we know where the root cause of this bug lies? Is it a problem in SyntaxGenerator? If we know we should file an issue and link to it in the workaround.

Can you add a test case that covers the scenario?

[andriipatsula]

@ericstj Thank you for the feedback. The problem is either in the Roslyn API or in the SBRP (Source-Build-Reference-Package) generator. I agree that the solution is not 100% clear and not in the best code style. I wrote an algorithm for the @MichaelSimons 's team how to build a local version of the GenAPI from the PR, prepare a nuget package and use it in the SBRP generator. I'll close this PR soon (without merging).

[ericstj]

@andriipatsula I'm OK with us taking the workaround, I was just hoping for a test case and an answer to those questions so that we can understand the urgency. I'll see if I can pick this up and fill in.

[ericstj]

I couldn't get this to fail. The following test passes for me: #31678

[ericstj]

It wasn't failing because we were testing with source symbols at this point. If we test wit metadata symbols it works correctly. I'll resurrect this workaround.