ApiDiff: Add AssemblySymbolLoader method, a package dependency from CodeAnalysis, and minor fixes

[carlossanlop]

This PR is part of the work needed to create an ApiDiff tool that reuses some of the code from Microsoft.DotNet.GenAPI. The idea is to make the larger PR smaller and make it easier to review: #45389

The purpose of this change is to:

• Add the dependency to Microsoft.CodeAnalysis.Workspaces.Common, as it will be used in the upcoming change. The files adding this dependency are often showing merge conflicts due to the packages above and below changing often, making it very difficult to keep the PRs up to date.
• Add an API that will be later be used to refactor some of the other methods in the same class.
• Some minor fixes of comments and typos.

[ViktorHofer]

Can you please describe why the new AssemblySymbolLoader API is necessary?

[carlossanlop]

Can you please describe why the new AssemblySymbolLoader API is necessary?

Sure: In the original PR I added a factory method to create an AssemblySymbolLoader instance. It uses this LoadAssembliesAsDictionary method. I added this factory method to the PR.

But I also noticed that I have simplified the ApiDiff tool enough to not need this method anywhere else. So I'll make it private, as I still need it for the factory method.

[ViktorHofer]

I was talking about this new public static method: public static (AssemblySymbolLoader, Dictionary<string, IAssemblySymbol>) CreateFromFiles(ILog logger, string[] assembliesPaths, string[]? assemblyReferencesPaths, bool respectInternals = false).

I would like to understand why AsmDiff needs a new entry point to AssemblySymbolLoader given that APICompat and GenAPI don't require it.

[carlossanlop]

I'll split this. Some things can be sent separately alongside a bigger change.