feat: add analyzer to detect and flag SuppressMessage attributes

[dnyw4l3n13]

Summary

Add a Roslyn analyzer rule that detects [SuppressMessage] attributes (and potentially #pragma warning disable) and reports them as errors, unless they are in an explicitly allowed list.

Background

Per project policy, warnings should never be suppressed without explicit permission. An analyzer to enforce this would prevent suppressions from being silently introduced by developers or AI agents.

This was raised from a code review on credfeto/credfeto-changlog-manager#281 where [SuppressMessage] was used to silence MA0045/VSTHRD002/CA2012 instead of fixing the underlying async code structure.

Proposed Behaviour

• Error when a [SuppressMessage] attribute is present on any type or member
• Optionally, an explicit allowlist of checkIds that are permitted (e.g. CA1812 for DI-registered internal classes)
• Should cover both attribute form ([SuppressMessage(...)]) and pragma form (#pragma warning disable XXXXX)

References

• feat: add rule to AI instructions prohibiting SuppressMessage without explicit permission credfeto/cs-template#781 — AI instructions rule to match

[credfeto]

Extend SuppressMessageDiagnosticsAnalyzer

need to be able to specify a list of places where it is valid for a suppression to appear..

e.g:

``pseudocode
[
{
category: "Roslynator.Analyzers",
checkId: "RCS1231",
whenAllowed: Function to determine if this is a whitelisted location,

Error To raise e.g. FFS1234 (or whatever the next sequence is)

}
]
``

e.g: this case where the analyzer isn't quite right

[SuppressMessage(category: "Roslynator.Analyzers", checkId: "RCS1231: Spans should be ref read-only", Justification = "Except when they're in a params parameter")]
private static IReadOnlyList<string> GetFiles(params ReadOnlySpan<string> searchPatterns){...}

additional whitelists need to be added easily.