The parent clock will not unpause until WaitingForFrames becomes false,
so I've moved the set of that before we start to propagate its values
across. Doesn't fix any visible issue but should make propagation one
game loop faster.
When `FrameStabilityContainer` decides it needs multiple updates on the same frame, it ends up with an elapsed time of zero. This was interacting badly with the condition used in `RulesetInputManager` to govern playback direction.
I have changed this to use `Rate` as exposed by the frame stable clock.
- Closes#6198.