Thoughts to reorganize rules in Performance chapter

[bkoelman]

Not all rules in this chapter are about performance. Some are about multi-threading and async/await:

• Only use async for low-intensive long-running activities (AV1820) This rule is about application responsiveness.
• Beware of mixing up async/await with Task.Wait (AV1830)
• Beware of async/await deadlocks in special environments (e.g. WPF) (AV1835) These rules are about correctness and attempt to protect against deadlocks.
• Await ValueTask and ValueTask<T> directly and exactly once (AV1840) Also about correctness.

On the other hand, the next rules concern performance, but are in a different chapter:

• Use generic constraints if applicable (AV1240) Aside from code readability, using type parameters with constraints avoids expensive casts and boxing.
• Evaluate the result of a LINQ expression before returning it (AV1250) The point is to avoid doing duplicate work and reuse cached data.
• Only use the dynamic keyword when talking to a dynamic object (AV2230) Dynamic is easy to write but performs poorly.

The next rules affect async/await, but are in a different chapter:

• Properly handle exceptions in asynchronous code (AV1215)
• Postfix asynchronous methods with Async or TaskAsync (AV1755)

I'm thinking we should have a chapter on Performance and one on Async/Threading. But of course, that would change the IDs of existing rules, which is problematic for https://www.nuget.org/packages/CSharpGuidelinesAnalyzer/, because developers have existing suppressions by rule ID in their codebases, which will break.

[dennisdoomen]

As discussed f2f, it seems that the impact on existing consumers of your analyzer would have to reconfigure their suppressions. It might be better to postpone that until the next major version.