Copy slow-motion related metadata to AMediaExtractor_getFileFormat

SEF slo-mo extract will put the slo-mo marker on file meta (instead
of track meta). Passthrough the slo-mo marker as well as layer count
on the NuMediaExtractor's getFileFormat.

bug: 160260201
test: locally apply the SEF extractor patch, and verify that
AMediaExtractor_getFileFormat can retrieve the slo-mo markers
and layer count info for SEF slo-mo clips.

Change-Id: I6497ec50ad8662425376d6c1924f75fd495fd71d