Roslyn analyzers are being run in excluded directories

**EDIT:** Issue title edited to reflect [the following](https://github.com/OmniSharp/omnisharp-vscode/issues/4718#issuecomment-919006432):

> > @RaZeR-RBI Sorry about that instead of generated_code = true, try setting dotnet_analyzer_diagnostic.severity = none. This should set all analyzers severity to none. (See https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/configuration-options#precedence)

> That helps with hiding the warnings in the 'Problems' tab (which I've done before by specifying a filter), but the analyzers are still being run in projects located in excluded folders.

> To paraphrase, the UI side of the issue can be fixed by using this option, but the performance side is, sadly, isn't solved.

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Apologies if it has been asked before or I'm reporting it to a wrong repository.

My current project uses a big amount of dependencies supplied in a source form instead of NuGet packages.
Solution load in VS Code takes several minutes and a lot of CPU power because of Roslyn analyzers trying to find issues in linked subprojects.

Is there a way to skip analysis in specific folders and/or projects?
They still should be loaded for Intellisense to work (I can't exclude them), but I'm not particularly interested of possible issues they may contain.

Thank you very much for your hard work.