Replace static code analysis to use `Microsoft.CodeAnalysis.NetAnalyzers` instead of FxCop

[marto83]

The FxCop and Microsoft.CodeAnalysis.Analyzers are now deprecated. We should move to using Microsoft.CodeAnalysis.NetAnalyzers and moving the rules into .editorconfig which will help IDEs enforce the rules too. The migration is described in https://docs.microsoft.com/en-us/visualstudio/code-quality/migrate-from-fxcop-analyzers-to-net-analyzers?view=vs-2022

Updating the analyzers might help with https://github.com/ably/ably-dotnet/issues/926

┆Issue is synchronized with this Jira Task by Unito

[QuintinWillison]

Further thoughts from @tomkirbygreen ...

Static Code Analysis for Pull Requests

We should enable GitHub Action hosted static code analysis for all pull requests (on-create and onupdate) utilizing at a minimum the latest Roslyn Analyzers. Ably may want to consider evaluating SonarQube as a cross SDK analysis platform as it provides support for pretty much all our core SDKs.