The `AudioProcessor` interface requires that no more input is queued after
queueing end of stream, but `DefaultAudioSink` did queue more input and the
implementation of `SonicAudioProcessor` actually relied on this to drain output
at the end of the stream.
Fix this behavior by getting `Sonic` output in `getOutput` and having
`DefaultAudioSink` only queue input to processors that are not draining.
Also add TODOs to clean up audio processor implementations where the code
handles interaction that doesn't conform to the interface.
PiperOrigin-RevId: 345406478
