Remove libmedia and libstagefright dependency from extractors

- MediaSource, DataSource and MediaExtractor are moved to
  libmediaextractor so that they can be used by extractor
  implementations without depending on libmedia and libstagefright.
- XXXFactory classes has been added in order not to expose CreateXXX
  methods in libmediaextractor.
- avc_utils is moved to libstagefright_foundation since most of
  extractor implementations are relying on that.

Test: build
Bug: 65851881

Change-Id: I654bd9e1433acf959a3dc65b9d4260f2dcacfda7