Agora RTC Objective-C API Reference Refactor

### - o -

- observationPosition : VideoTrackInfo
- opened : LiveStreamAdvancedFeature
- OPTIONAL_ENUM_SIZE_T : AudioPcmFrame , VideoFormat
- options : WatermarkConfig
- ordered : DataChannelConfig , DataStreamConfig
- orientationMode : RtmpStreamingVideoConfiguration , VideoEncoderConfiguration
- outputNumberOfChannels : AudioSessionConfiguration
- overrideSpeaker : AudioSessionConfiguration
- owner : PublisherConfiguration , AList< T >
- ownerUid : VideoTrackInfo