[Feature] - Track clock time for each screenshot in film strip

[matthew-carroll]

Film strips are sometimes used to create animation timelines. It may be useful in these timelines to know the timestamp for every frame. This way, viewers can tell roughly how fast the animation plays, and also whether the animation series is linear playback or accelerates/decelerates during capture. In fact, with this info, the timeline can chart the passage of time so see whether its linear or non-linear.

My initial thought is that this could be done with a WidgetTester decorator that intercepts all calls. But not sure.