Consider how should Scope be treated for UnconditionalSuppressMessage

Scopes are only relevant on the context of global unconditional suppressions -- and they are only ever used to check if a valid scope was used. The original intention of the property was to use it to check whether the target where a suppression is enacted is indeed a type or a member, but because we use [documentation format](https://github.com/dotnet/csharplang/blob/main/spec/documentation-comments.md#id-string-format) on the target this is not needed at all (since the target must be a fully-qualified string prepended with `T`, `M`, `F`, etc. letting it know the parser whether it is a type, method, field, and so on).

This rises the question of whether the `Scope` property of `UnconditionalSuppressMessage` should either be ignored or checked against the target (even though this is currently not needed for the above reasons; although we could expand the understood `Target` strings by using other parsers such as `System.Reflection.Runtime.TypeParsing`).