C#: Make sure allFeeds contains at least explicitFeeds

[mbg]

This (sort of) fixes a (sort of) bug in the computation of allFeeds. We assume that allFeeds includes explicitFeeds and that is generally true, except for one case. On systems with case-sensitive file systems, we may discover a configuration file such as Nuget.Config, which is not recognised by dotnet nuget list source (which e.g. only recognises NuGet.config and nuget.config). In that case, our call to GetNugetFeeds will retrieve the feeds from that file (because it is accepted when provided explicitly as --configfile argument), but the call to GetNugetFeedsFromFolder will not.

Arguably, another option here would be to make our configuration file discovery more strict and only recognise the same case-sensitive filenames as dotnet nuget list source. However, that may catch out customers by surprise who normally work on case-insensitive systems, but who use Default Setup.

Note that this doesn't address scenarios where GetNugetFeedsFromFolder misses feeds from parent directories because they have names that dotnet nuget list source doesn't recognise.

[Copilot]

Pull request overview

This pull request fixes a bug in the computation of allFeeds in the NuGet package restoration logic. The PR ensures that allFeeds always includes explicitFeeds, which is normally the case except when configuration files with non-standard casing (like Nuget.Config instead of nuget.config) are encountered on case-sensitive file systems.

Changes:

• Added logic to explicitly union explicitFeeds into allFeeds to handle the edge case where case-sensitive filesystems cause dotnet nuget list source to miss configuration files that are otherwise valid
• Added comprehensive comments explaining the rationale and the specific edge case being addressed

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[michaelnebel]

That is some excellent 🕵️ work!!!

[michaelnebel]

We should also run DCA.

[michaelnebel]

Fantastic!
Thank you!