This behavior was previously available as opt-in via
`MediaItem.DrmConfiguration.Builder.setPlayClearContentWithoutKey` and
`DefaultDrmSessionManager.Builder.setPlayClearSamplesWithoutKeys`. This
change flips the default of both these properties to true.
This should speed up the time for playback to start when playing DRM
content with a 'clear lead' of unencrypted samples at the start.
Previously playback would wait until the keys for the later encrypted
samples were ready. The new behaviour could result in mid-playback
stalls/rebuffers if the keys are not ready yet by the transition from
clear to encrypted samples, but this is not really a regression since
previously playback wouldn't have started at all at this point.
PiperOrigin-RevId: 595992727
77f311917f