transcoding: use NDK methods for permission and binder

- Change permission checks to use NDK
- Replace MediaProvider uid check with permission check of
  MANAGE_EXTERNAL_STORAGE (which is replacing the deprecated
  WRITE_MEDIA_STORAGE).
- Use ABinderProcess_* for thread pool.

bug: 159172726
bug: 171393067
test: MediaTranscodingService unit tests; dumpsys to check if
MediaProvider can still regiserClient successfully.

Change-Id: I4fed7bb23a2d68c92e5cd1aecd5a6ef340dc2b61