Analyzer for detecting use of Headers[int]

[adityamandaleeka]

If someone is using the adapters and using Headers[int] we should flag it and tell them to index by string. This will also be seen if you enumerate the collection.

Low priority for now since we haven't seen it in the wild.

[timmydo]

I just tried this out: https://github.com/dotnet/roslyn-analyzers/blob/main/src/Microsoft.CodeAnalysis.BannedApiAnalyzers/BannedApiAnalyzers.Help.md to track down the usage:

M:System.Collections.Specialized.NameValueCollection.Get(System.Int32);Don't use BannedType
M:System.Collections.Specialized.NameValueCollection.GetKey(System.Int32);Don't use BannedType
M:System.Collections.Specialized.NameValueCollection.GetValues(System.Int32);Don't use BannedType
M:System.Collections.Specialized.NameValueCollection.Keys;Don't use BannedType

I've found about 10 usages in the csproj I'm working on now. Will scan the other 2k csprojs and see how bad it gets.