Get the currently playing interstitial ad or ad the identificator to shaka.ads.InterstitialAd

[npovsic]

Have you read the FAQ and checked for duplicate open issues?
Yes.

Is your feature request related to a problem? Please describe.
I am attempting to implement VMAP/VAST ads to the player. It says it supports them but without tracking. Since this is a requirement, I need to handle the tracking events myself.

I implemented a VMAP/VAST parser to get all the interstitials and add them using the addCustomInterstitial method. The ads play correctly however I cannot access which interstitial is playing so that I can match the tracking event URLs. The value is available in the InterstitialAdManager lastPlayedAd_ value but that is not exposed.

This is the example of a VAST that I am using: VAST with tracking events.

Describe the solution you'd like
I would like to access at least the ID of the current interstitial, so if that could be exposed in the same way as this issue #7793 that would be great.