Update of FeatureContributionCalculation to new API

[artidoro]

Fixes #1791.

As this is a WIP PR, I am still completing the work, but I would really appreciate your feedback on what I have done so far.

In this PR:

• I created a new ITransformer for FeatureContributionCalculation (previously known as WhatTheFeature) by converting previous ISchemaBoundRowMapper to two separate classes: a IRowMapper and a ISchemaBoundMapper.
• I created a new IEstimator that produces the transformer.
• I added tests for the Transformer and Estimator. (Need to add a few more)
• I added MlContext extensions.
• I added documentation, and checks for arguments and types.

Will do in a separate PR:

• Add static extensions for the estimators.
• I allowed pipelines, and not just IPredictor, to be passed to the IEstimator.

[rogancarr]

I did a non-technical pass over to look at usability. Overall, this looks good! Mostly, I'd like to make sure we can use it in pipelines and that we have tests that cover the options and the implementations. (Although maybe implementation tests can be a separate PR.)

[Ivanidzo4ka]

            Console.WriteLine("{0:0.00}\t{1:0.00}\t{2}\t{3:0.00}\t{4:0.00}\t{5:0.00}\t{6:0.00}",

I think we tend to put results of output into comments for the file. #Resolved

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Refers to: docs/samples/Microsoft.ML.Samples/Dynamic/FeatureContributionCalculationTransform.cs:87 in a62a510. [](commit_id = a62a510, deletion_comment = False)