Error message for non-parsable datasets in AutoML

[justinormont]

Fixes: #5129

I'd recommend improving the current error message:

machinelearning/src/Microsoft.ML.AutoML/ColumnInference/ColumnInferenceApi.cs

Lines 120 to 123 in e5a19af

	if (!splitInference.IsSuccess)
	{
	throw new InferenceException(InferenceExceptionType.ColumnSplit, "Unable to split the file provided into multiple, consistent columns.");
	}

It currently says, "Unable to split the file provided into multiple, consistent columns.", which is rather uninformative and non-actionable.

Perhaps, as I think @briacht is suggesting, have it list the acceptable file formats we can parse: "Unable to split the file provided into multiple, consistent columns. Readable formats include delimited files such as CSV/TSV. Check for a consistent number of columns and proper escaping and quoting.".

This messaging now includes, the problem, and next steps for the user.

I mention delimited as AutoML supports more than CSV/TSV as it tries tab, comma, space, semi-colon as the separator (src). If we run into other common separators, we can trivially augment this list. One candidate is the vertical bar |.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@a2406f6). Click here to learn what that means.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##             master    #5130   +/-   ##
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  Coverage          ?   75.60%           
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  Files             ?      990           
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  Hits              ?   135481           
  Misses            ?    38465           
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Flag	Coverage Δ
#Debug	75.60% <0.00%> (?)
#production	71.50% <0.00%> (?)
#test	88.85% <ø> (?)

Impacted Files	Coverage Δ
...ft.ML.AutoML/ColumnInference/ColumnInferenceApi.cs	83.00% <0.00%> (ø)

[harishsk]