First draw instrumentation

[Doohl]

It would be nice to have signals on how long it takes for Activities (and Fragments?) to become interactive for the user. The Android vitals documentation specs out two vitals:

• TTID - Time to initial display (AKA "time to first draw"), which is the time it takes to display the first frame of the UI
• TTFD - Time to full display, which is the time it takes for the app to become fully interactive for the user.

TTFD depends on the app reporting when a component's fully drawn (all async fetches resolved, etc): https://developer.android.com/reference/androidx/activity/ComponentActivity#reportFullyDrawn()

TTID is much easier to automatically instrument within our existing Activity lifecycle. We can rely on ViewTreeObserver.addOnDrawListener to report on Activity first draw. We can remove the listener after the first draw to avoid reports on subsequent draws, since the first draw is the most important.