nuplayer: Pass along the sniffed metadata from GenericSource

 * When the extended sniffer detects a file type that only it can
   handle, it will set a flag in the metadata. In some cases,
   an extractor exists in Android already for the filetype however
   it may be known to fail or we may want different behavior.
 * This flag is checked in MediaExtractor, but GenericSource does
   a little dance in order to stack DataSources for DRM and was
   throwing out this metadata (it's not really used by AOSP), so
   the desired behavior was not seen for some cases.
 * Add a new optional argument when creating the MediaExtractor to
   pass in the metadata from the original sniff so that the extended
   extractor is used where necessary for streaming formats.
 * This fixes FLAC offload with Tidal.

Change-Id: I7d6b875346ce63b60cd3c37572b779665bfe217c