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
- bundleCode : AgoraMetachatAvatarModelInfo , AgoraMetachatBundleInfo
- bundleId : AgoraMetachatBundleInfo
- bundleName : AgoraMetachatBundleInfo
- bundlePath : AgoraMetachatBundleInfo
- bundles : AgoraMetachatSceneInfo
- bundleSize : AgoraMetachatBundleInfo
- bundleType : AgoraMetachatBundleInfo
- bytesPerSample : AgoraAudioFrame , AgoraAudioPcmFrame