F#: struct DUs and Records should use the Struct attribute in the signature

[cartermp]

Example:

This type is actually declared in source as:

    [<StructuralEquality; StructuralComparison>]
    [<CompiledName("FSharpResult`2")>]
    [<Struct>]
    type Result<'T,'TError> = 

      /// Represents an OK or a Successful result. The code succeeded with a value of 'T.
      | Ok of ResultValue:'T 

      /// Represents an Error or a Failure. The code failed with a value of 'TError representing what went wrong.
      | Error of ErrorValue:'TError

The Struct attribute should be listed in the API reference signature.

The other two should be ignored.