Codecs: Add MetaDataMode support to software video encoders.

This support is needed to enable efficient video recording with
emulator and camera HAL 2.

- Update SoftAVCEncoder and SoftMPEG4Encoder to support MetaDataMode
  extension.
- Allow CameraSource to handle opaque pixel formats, so that
  MetaDataMode can be used.
- Remove hardware codec restriction for MetaDataMode

Bug: 6243944
Change-Id: I970eb3d55542a413b6d75a78f76d3a8583155601