When we add DRM pre-acquire support to SampleQueue, we'll dispatch
twice the number of acquire and release events. This is slightly
confusing, since there's the same number of
DrmSessionManager#acquireSession() calls.
We can mitigate this by only dispatching each acquire and release
event to at most one EventDispatcher.
This also changes the events fired when playing a stream with both audio
and video encrypted with the same keys (even without pre-acquisition).
Before: The EventDispatcher would see 2 aquires, 1 key load and 2
release events.
After: The EventDispatcher will see 1 acquire, 1 key load and 1 release.
PiperOrigin-RevId: 358804502
