Any calls that issue a `seekTo()` where the position is `TIME_UNSET` will
now restore the live offset target to the MediaItem set default.
The change simply passes a flag to `updatePlaybackSpeedSettingsForNewPeriod()` that
indicates the call is from a seek operation. If this flag is set, a `positionForTargetOffsetOverrideUs`
of `TIME_UNSET` unconditionally removes the `setTargetLiveOffsetOverrideUs()`
This fixes issue #11050
