GenAPI can generate ambiguous call to base constructor

When GenAPI defines arguments to a base constructor, it uses default! but this can lead to an ambiguous call when the base type has constructor overloads with the same number of parameters but different types.

An example of this is the generated code for NuGet.Protocol.6.5.0:

public partial class SourcePackageDependencyInfo : Packaging.Core.PackageDependencyInfo
{
    public SourcePackageDependencyInfo(Packaging.Core.PackageIdentity identity, System.Collections.Generic.IEnumerable<Packaging.Core.PackageDependency> dependencies, bool listed, SourceRepository source, System.Uri downloadUri, string packageHash) : base(default!, default!) { }

This leads to the following compiler error:

error CS0121: The call is ambiguous between the following methods or properties: 'PackageDependencyInfo.PackageDependencyInfo(PackageIdentity, IEnumerable<PackageDependency>)' and 'PackageDependencyInfo.PackageDependencyInfo(string, NuGetVersion)

This can be solved by explicitly casting default to the desired type:

: base((Packaging.Core.PackageIdentity)default!, (System.Collections.Generic.IEnumerable<Packaging.Core.PackageDependency>)default!) { }

cc @andriipatsula @ViktorHofer

[ericstj]

https://github.com/dotnet/sdk/blob/dabb52e63c2a171bdf519d2123470a260d6d1cb4/src/Tests/Microsoft.DotNet.GenAPI.Tests/CSharpFileBuilderTests.cs#L1466

[ericstj]

Fix is in https://github.com/dotnet/roslyn/pull/67893. Once we can get a new build of roslyn with this fix in SDK we can resolve this (and re-enable the test).