Analyzer: VB support

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Our analyzer currently depends on C# and VB language nugets, but one of these languages isn't in use. See #21996 (comment) for a possible way to do this (/cc @jmarolf)

The VB capabilities of the analyzer are being removed for 5.0 via #22211, because of issues with referencing both language assemblies (see #22177). @sharwell has submitted #22195 (thanks!), which splits the analyzer and allows proper support for both C# and VB. Aside from that PR, for better VB support we'd identify more VB syntax patterns and narrow them down when reporting diagnostics (as we already do with C#).