Real apps probably aren't going to be allowing playback speed to be
set to anything other than the options listed in their UI, and so
this is not worth the complexity.
It also violates the idea that the UI should look the same regardless
of when the player is set on the view, since if it's set and then the
playback speed is changed to a listed option then the custom speed
remains, where-as if the speed is changed to a listed option and then
it's set, the custom speed will not be shown.
PiperOrigin-RevId: 343260450
