Slow render spans don't provide data of current screen

[jitinsharma]

Currently Span generated by Slow Render Instrumentation just provides activity name, which is very limited information since activity itself might render multiple fragments, views, popups etc. We can use VisibileScreenDetector to add current screen and last screen as span attributes which might give a more approximate answer where frozen frame was detected. I can try out a POC around how accurately can we get screen data since FrameMetrics listener is attached at activity, but would like to know any other thoughts around this.