Bug: Should not report AV1553 on overridden members

[bkoelman]

Rule: AV1553 Do not use optional parameters with default value null for strings, collections or tasks

For example:

• when inheriting from abstract class Microsoft.AspNetCore.Routing.LinkGenerator
• when implementing interface Swashbuckle.AspNetCore.Swagger.ISwaggerProvider

These require to implement methods with optional parameters. There's no way to fix the reported violation, other than to suppress it. Therefore it doesn't make sense to report a violation in these cases.