weighting parameter value lost for ProduceWordBag call

[MarcinJuraszek]

When calling ProduceWordBags with weighting parameter specified it gets lost and the results always use WeightingCriteria.Tf.

The simplest repro-steps I have (based on LdaTransform sample):

// Get a small dataset as an IEnumerable and then read it as a ML.NET data set.
IEnumerable<SamplesUtils.DatasetUtils.SampleTopicsData> data = SamplesUtils.DatasetUtils.GetTopicsData();
var trainData = ml.Data.LoadFromEnumerable(data);

string review = nameof(SamplesUtils.DatasetUtils.SampleTopicsData.Review);

// A pipeline for featurizing the "Review" column
var pipeline = ml.Transforms.Text.ProduceWordBags("bags", review, ngramLength: 1, weighting: Transforms.Text.NgramExtractingEstimator.WeightingCriteria.TfIdf);

// The transformed data
var transformer = pipeline.Fit(trainData);
var transformed_data = transformer.Transform(trainData);

var preview = transformed_data.Preview();

var bagsColumn = transformed_data.GetColumn<VBuffer<float>>("bags");
foreach (var featureRow in bagsColumn )
{
    foreach (var value in featureRow.GetValues())
        Console.Write($"{value} ");
    Console.WriteLine("");
}

Expected output:

1.386294 0.6931472 0.6931472 1.386294 0.6931472 0.2876821 0 0 0 0 0 0 0
0 0.6931472 0.6931472 0 0.6931472 0.2876821 1.386294 1.386294 0 0 0 0 0
0.6931472 0.6931472 0.6931472 0.6931472 0.6931472
0 0 0 0 0 0.2876821 0 0 0.6931472 0.6931472 0.6931472 0.6931472 0.6931472

Actual output:

1 1 1 1 1 1 0 0 0 0 0 0 0
0 1 1 0 1 1 1 1 0 0 0 0 0
1 1 1 1 1
0 0 0 0 0 1 0 0 1 1 1 1 1

I'll send a PR with a fix shortly.