Improve exception msg by adding column name

[wangyems]

For the issue #5211

In this case, when user choose a big dataset and one or more columns have more than expected unique values, the crossvalidate() method throws overflow but it's difficult for users to realize which column in the dataset cause the problem. If we append column name to the overflow message, user can quickly find where goes wrong.

[codecov]

Codecov Report

Merging #5232 into master will increase coverage by 0.00%.
The diff coverage is 89.47%.

@@           Coverage Diff           @@
##           master    #5232   +/-   ##
=======================================
  Coverage   73.47%   73.47%           
=======================================
  Files        1010     1010           
  Lines      187988   188029   +41     
  Branches    20262    20266    +4     
=======================================
+ Hits       138118   138150   +32     
- Misses      44385    44390    +5     
- Partials     5485     5489    +4     

Flag	Coverage Δ
#Debug	73.47% <89.47%> (+<0.01%)	⬆️
#production	69.28% <100.00%> (-0.01%)	⬇️
#test	87.38% <82.60%> (+<0.01%)	⬆️

Impacted Files	Coverage Δ
...ML.Tests/Transformers/KeyToVectorEstimatorTests.cs	97.64% <82.60%> (-2.36%)	⬇️
src/Microsoft.ML.Data/Transforms/KeyToVector.cs	83.91% <100.00%> (+0.24%)	⬆️
....ML.AutoML/PipelineSuggesters/PipelineSuggester.cs	79.83% <0.00%> (-3.37%)	⬇️
...rc/Microsoft.ML.Featurizers/DateTimeTransformer.cs	87.15% <0.00%> (-1.81%)	⬇️
src/Microsoft.ML.Maml/MAML.cs	24.75% <0.00%> (-1.46%)	⬇️
...Microsoft.ML.Transforms/OptionalColumnTransform.cs	76.87% <0.00%> (-0.87%)	⬇️
...soft.ML.Data/DataView/DataViewConstructionUtils.cs	85.51% <0.00%> (+0.02%)	⬆️
src/Microsoft.ML.Core/Data/Repository.cs	79.77% <0.00%> (+0.05%)	⬆️
test/Microsoft.ML.Functional.Tests/ModelFiles.cs	96.38% <0.00%> (+0.12%)	⬆️
...soft.ML.Data/DataLoadSave/Text/TextLoaderCursor.cs	89.45% <0.00%> (+0.15%)	⬆️
... and 3 more

[harishsk]