In 2.11.2 to 2.11.5, we considered all AAC streams as consisting
only of sync samples. In 2.11.6+, we considered no AAC streams as
consisting of sync samples, because the property is not guaranteed
specifically for xHE-AAC. This will have caused a small regression
is seek speed for some types of media.
This change brings back the optimization for AAC, specifically
excluding only xHE-AAC (and cases where we don't know what type of
AAC we're dealing with).
PiperOrigin-RevId: 328950697
