[tvOS IMA SDK] no STARTED event from AdsManager with specific ad

[David Steinacher]

Hi,

We discovered that the `IMAAdsManager` does not emit the `kIMAAdEvent_STARTED` event for certain VAST tags.

We drilled it down to the existence of a certain VAST extension. When there is a VAST Extension with `type="sodar"`, no more `kIMAAdEvent_STARTED` is received despite the ad starting playback as expected. All other events, and also time updates, are received as expected. The same VAST tag plays fine on iOS as well.

We were testing with:

- GoogleAds-IMA-tvOS-SDK: 4.13.0

I added an adapted version of the Swift BasicExample application from googleads/googleads-ima-ios and added tvOS support as the googleads/googleads-ima-tvos-client-side is not plug-and-play ready.

In this sample application, I added a log output to the `adsManager(_ adsManager: IMAAdsManager, didReceive event: IMAAdEvent)` delegate method, where you can see that the started event is not received. To run the sample application, download it and run `pod install`.

The example tag and an example application can be found in the attachments.