Allow NuGet dependencies to exist with duplicate names but different dependency types

[DavidBoike]

• Fixes Closing .NET PRs as "no longer needed" when dependency is still present and out-of-date #9612 and Unhandled exception: System.ArgumentException: An item with the same key has already been added. #9495

NuGetUpdater.Cli.exe discover was throwing "An item with teh same key has already been added" in the situation where a centrally-managed Directory.Build.props file would have 2 references for the same package based on a condition such as the repository using central package management.

This is an example that would make the tool throw from my company's centrally-managed Directory.Build.props file:

<ItemGroup Condition="'$(ManagePackageVersionsCentrally)' == 'true'">
  <GlobalPackageReference Include="Particular.Analyzers" Version="$(ParticularAnalyzersVersion)" />
</ItemGroup>

<ItemGroup Condition="'$(ManagePackageVersionsCentrally)' != 'true'">
  <PackageReference Include="Particular.Analyzers" Version="$(ParticularAnalyzersVersion)" PrivateAssets="All" />
</ItemGroup>

If central package management is enabled, then our company-managed Roslyn analyzers package is included as a GlobalPackageReference. If not, it's added to the project as a regular PackageReference.

But the duplicate name caused a problem with the discover code tried to do .ToDictionary(…) on the name alone, so this change uses a lookup to allow multiple values.

A test has been added that demonstrates the desired result.

[DavidBoike]

I see that one of the tests in Specs / ci (nuget, nuget, nuget) is failing. I don't grok Ruby or RSpec very well, unfortunately, but I do see that the most recent run on main also had a failure in that test suite, although it's a different test. I don't know if the RSpec tests even run NuGetUpdater.Cli (I can't find any evidence that it does?) but I did take the failure I saw (getting 5 dependencies out of a 9-dependency packages.config file) and set up a different test in the .NET project tests, and the updater was still coming up with 9 dependencies there, so I don't know what's up with that.

[DavidBoike]

Must have been a heisenbug, there was a new commit to main, and after I rebased all the tests came up green.

[brettfo]

@DavidBoike If you curious for the future, this repo only invokes the Ruby unit tests so to include the C# tests we got sneaky and run dotnet test ... here.