The main target of this task is to uniform and modernize our current tooling we use for code style. 

Today our style rules live in .editorconfig but don't actually run during the build (they only appear as hints in the IDE) while our code-quality rules are enforced through five separate .ruleset files and the now-deprecated FxCopAnalyzers package. We would like for the deterministic rules to be enforced on build/CI and modernize our current tooling. 

The targets are:

• Drop the deprecated FxCopAnalyzers package in favour of the analyzers built into the .NET SDK.
• Move the rules from the five .ruleset files into .editorconfig and retire them. .ruleset is the old mechanism, superseded by .editorconfig, and consolidating keeps all the rules in one place.
• Turn on EnforceCodeStyleInBuild so the style rules run in the build, not just the IDE. 
• Add dotnet format --verify-no-changes to CI. It reads the same .editorconfig and fails the build on drift, so configuration and enforcement can't diverge.

This ticket will keep the set of rules the same, it's just about the tooling.