handleSourceInfoRefreshed checks for various conditions which may trigger a
change in position. In all cases, we need to resolve the new position for ads,
and if the corresponding MediaPeriods already exist, perform the seek to the new
position.
This change simplified the code by
1. Moving all conditions in a single if-else structure which just determines
the new playback position. This makes it easier to read and to follow.
2. Doing the subsequent seek and position update in one final step to remove
duplicated code.
As a side effect, it also improves some edge cases. For example when skipping
an ad to an already prebuffered period, we now properly update the existing
prebuffered period.
PiperOrigin-RevId: 243588014
75238e5e4f