OnSeekProcessed is documented to be called as soon as all neccessary state changes
as a result of the seek have been made. As we now mask the state changes directly
when calling seekTo, we can also call this callback immediately without changing
the semantics of the method.
Our tests often use this callback as a way to wait for the internal player
to receive all pending commands and then report back. This is a special test
requirement for cases where we want to make sure no further updates happen as
a result of the player handling commands. To facilitate that, a new action is
added with a more descriptive name that achieves the same goal.
PiperOrigin-RevId: 303296210
af05ceac61