AutoML execute with preFeaturizer should accept Int32 and so

### System information

Microsoft.ML.AutoML (0.14.0)

### Issue

**TL;DR:** `ExperimentBase.Execute` with non-null `preFeaturizer` argument should check the schema types **after** transforming the `preFeaturizer`.

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I have a flattened object with `long` and `int` fields that I load it to an `IDataView`.
If I want to `Execute` an experiment for this `dataView`, I get this expeption:

> **System.ArgumentException:** 'Only supported feature column types are Boolean, Single, and String. Please change the feature column Feature1 of type Int64 to one of the supported types.
Parameter name: trainData'

So, I have to create an `EstimatorChain` to `ConvertType` from `long` to `Single`, and `Fit` then `Transform` the `dataView`.

Let's say I have this `EstimatorChain` to transform these types. Now I have two options:

1. Transform the `dataView` **before** passing it to the `Execute` method.
With this option, the problem is that I have to create a class that fit to the new schema, if I want to save the model and use it latter.
(The first generic type in `CreatePredictionEngine` must be appropriated to the `inputSchema`)
2. Pass this `EstimatorChain` as `preFeaturizer` argument in the `Execute` method.
But this is not a real solution because the `Execute` method **still throws the exception above!**