stagefright: untangle metadata-mode handling

- specify requested metadata mode from producers to OMX
- (pass requested metadata in IOMX::storeMetadataInBuffers)
- use correct logic for native handle source
- use native handle source for encoded meta buffers

Bug: 22775369
Change-Id: I58b03acd3e9a5367d5010d7f87b7af5cae23362c
17 files changed