New PFI API (#5934)

Author: michaelgsharp

src/Microsoft.ML.Data/Prediction/CalibratorCatalog.cs

@@ -162,7 +162,7 @@ public CalibratorTransformer<TICalibrator> Fit(IDataView input)
     /// where score can be viewed as a feature while probability is treated as the label.
     /// </summary>
     /// <typeparam name="TICalibrator">The <see cref="ICalibrator"/> used to transform the data.</typeparam>
-    public abstract class CalibratorTransformer<TICalibrator> : RowToRowTransformerBase, ISingleFeaturePredictionTransformer<TICalibrator>
+    public abstract class CalibratorTransformer<TICalibrator> : RowToRowTransformerBase, ISingleFeaturePredictionTransformer<TICalibrator>, ISingleFeaturePredictionTransformer
         where TICalibrator : class, ICalibrator
     {
         private readonly TICalibrator _calibrator;
@@ -201,6 +201,7 @@ private protected CalibratorTransformer(IHostEnvironment env, ModelLoadContext c
         }
 
         string ISingleFeaturePredictionTransformer<TICalibrator>.FeatureColumnName => DefaultColumnNames.Score;
+        string ISingleFeaturePredictionTransformer.FeatureColumnName => ((ISingleFeaturePredictionTransformer<TICalibrator>)this).FeatureColumnName;
 
         DataViewType ISingleFeaturePredictionTransformer<TICalibrator>.FeatureColumnType => NumberDataViewType.Single;
 

src/Microsoft.ML.Data/Prediction/IPredictionTransformer.cs

@@ -34,4 +34,16 @@ public interface ISingleFeaturePredictionTransformer<out TModel> : IPredictionTr
         /// <summary>Holds information about the type of the feature column.</summary>
         DataViewType FeatureColumnType { get; }
     }
+
+    /// <summary>
+    /// An ISingleFeaturePredictionTransformer contains the name of the <see cref="FeatureColumnName"/>
+    /// and its type, <see cref="FeatureColumnType"/>. Implementations of this interface, have the ability
+    /// to score the data of an input <see cref="IDataView"/> through the <see cref="ITransformer.Transform(IDataView)"/>
+    /// </summary>
+    [BestFriend]
+    internal interface ISingleFeaturePredictionTransformer : ITransformer
+    {
+        /// <summary>The name of the feature column.</summary>
+        string FeatureColumnName { get; }
+    }
 }

src/Microsoft.ML.Data/Scorers/PredictionTransformer.cs

@@ -204,7 +204,7 @@ public void Dispose()
     /// Those are all the transformers that work with one feature column.
     /// </summary>
     /// <typeparam name="TModel">The model used to transform the data.</typeparam>
-    public abstract class SingleFeaturePredictionTransformerBase<TModel> : PredictionTransformerBase<TModel>, ISingleFeaturePredictionTransformer<TModel>
+    public abstract class SingleFeaturePredictionTransformerBase<TModel> : PredictionTransformerBase<TModel>, ISingleFeaturePredictionTransformer<TModel>, ISingleFeaturePredictionTransformer
         where TModel : class
     {
         /// <summary>