This restructure moves all the position resolving code to a static method and
removes the dependency of the MediaPeriodQueue on having an up-to-date timeline.
Both steps allow simplified reasoning about the code as the static method can't change
the state of the player, and there is no risk the queue can use the wrong timeline.
These propoerties allow to fix a bug causing inconsistent states in a follow-up step.
PiperOrigin-RevId: 290616395
21c76b012c