onCurrentFrameRendered should join multiple calls into a single post

[pyricau]

Current impl:

internal fun onCurrentFrameRendered(callback: (Long) -> Unit) {
  mainHandler.postAtFrontOfQueueAsync {
    val frameRenderedUptimeMillis = SystemClock.uptimeMillis()
    callback(frameRenderedUptimeMillis)
  }
}

This should be stateful and aware of any pending calls so that we only register a single call and a single uptime and dispatch to all callbacks