SDK / exoplayer

This makes the reading period advance early as expected at the end of an ad
period. Before this change the reading position of the metadata renderer
prevented advancing the period until metadata arrived after the start position of
the following period. Only then the reading position of the metadata renderer
is updated and beyond the start position of the following period which is a
condition to advance the reading period.

Because transitioning to the next period is a virtual transition and the
SharedMediaPeriod keeps reading from the same underlying sample streams, the
metadata renderer can safely be ignored for this check.

#minor-release

PiperOrigin-RevId: 432646037