Convenient way of providing LDA topic summary

[abgoswam]

In the LdaTransform, the details of the learnt model are contained in the LdaState object. When the user wants to introspect the LDA model learnt during the transformation, we return a topic summary vector .

We need to find a proper way of returning topic summary information to the user. Specifically the words that map to the topic summary vector

For this we need to figure out how to extract details from the LdaState object using C#. Currently LdaState invokes native code behind the scenes to get model info.

[abgoswam]

It turns out this can be handled by mapping slot names from the input schema during training. I have taken care of this in PR #1410

[abgoswam]

PR #1410 took care of this

[najeeb-kazmi]

This is again an issue since the PigSty API was removed. This functionality is no longer available in the Dynamic API. #4322 tracks all the issues filed for LDA topic summary.