Introduction of solution info and project file info

[Corniel]

Both SolutionInfo and ProjectInfo are immutable objects, describing the solution and its projects under analysis. They reflect the information resolved by calling MS's SolutionFile, and our own ProjectFile. As a result two properties of IAnalyzerManager are marked as obsolete.

This should also close #303

Before this can be finished, first #316 should be completed.

As this build now fails due to the issue reported at #328, also build dependency updates are included.

[Frulfump]

Since dotnet/sdk#50022 is now fixed and a part of .NET 10 this is even more relevant hoping you get the review you were looking for in #304 (comment)

[baronfel]

I'm confused - this PR doesn't add SLNX support at all? Or are you intending to introduce this as an 'abstraction' and then convert SolutionInfo over into being based on the Microsoft.VisualStudio.SolutionPersistence models?

[Corniel]

@baronfel Originally, this PR had nothing to do with SLNX support. But I'll update this PR so that the SolutionInfo is an immutable abstraction that both can deal with .sln and .slnx files.

[Corniel]

@Frulfump and @baronfel I've updated the implementation, now to support SLNX. It is not perfect (yet) but it is worth a try I guess.

[kudima03]

Hi @josephwoodward @phmonte,
many dependent projects are now in need of slnx support, especially with the release of .NET 10.
Could you please review the PR when you have a moment?

[Corniel]

@kudima03 I would urge you to also give some feedback/review. The more people who check a PR, the better.

[AlbertoMonteiro]

LGTM