SDK / exoplayer

The MockPlayer has a single CountDownLatch field and multiple boolean
flags that track if a player method was called. Upon calling the methods
the latch count. Tests set the latch count to match exactly with the
number of expected player interactions then block the test thread until
the latch reaches zero and assert the respective method flags are true.

This is subject to false positives. If the underneath implementation
changes and call more player method, then the test thread will unblock
as soon as a certain number of interactions is performed, which may be
less than what the test expected originally. However, the test may stil
pass if the player thread had enough time to update the expected method
flag.

This change removes the single CountDownLatch and the boolean flags and
instead it adds APIs to query the MockPlayer if a method has been called
and await until a method is called. Internally, the MockPlayer has a
ConditionVariable per method.

PiperOrigin-RevId: 432399077