Agora RTC Objective-C API Reference Refactor

### - b -

- backgroundColor : AgoraRtcVideoCanvas
- backgroundSourceType : AgoraVirtualBackgroundSource
- bandwidth : AgoraMvProperty
- bandwidthEstimationBps : AgoraDownlinkNetworkInfo
- beatsPerMeasure : AgoraRhythmPlayerConfig
- beatsPerMinute : AgoraRhythmPlayerConfig
- bitrate : AgoraScreenCaptureParameters , AgoraScreenVideoParameters
- bitrateInKbps : AgoraMediaPlayerSrcInfo
- blurDegree : AgoraVirtualBackgroundSource
- buffer : AgoraAudioFrame , WatermarkBuffer , WatermarkConfig
- bundleCode : AgoraMetaAvatarModelInfo , AgoraMetaBundleInfo
- bundleId : AgoraMetaBundleInfo
- bundleName : AgoraMetaBundleInfo
- bundlePath : AgoraMetaBundleInfo
- bundles : AgoraMetaSceneInfo
- bundleSize : AgoraMetaBundleInfo
- bundleType : AgoraMetaBundleInfo
- bytesPerSample : AgoraAudioFrame , AgoraAudioPcmFrame