Document new IDE rules #44420
Description
Describe the issue or suggestion
See https://github.com/dotnet/roslyn/blob/main/src/Features/RulesMissingDocumentation.md (although some of these are already doc'd).
- IDE0121
- IDE0340
- IDE0350
- IDE1007 (old analzyer error ID - won't add docs)
- IDE2000-2006 (old experimental formatting IDs - won't add docs)
- IDE3000 - Very new; tracked separately by Add docs for IDE3000 - Implement method with Copilot #45530