Agora RTC Objective-C API Reference Refactor

Here is a list of all functions, variables, defines, enums, and typedefs with links to the files they belong to:

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- SegModelAgoraAi : AgoraEnumerates.h
- SegModelAgoraGreen : AgoraEnumerates.h
- SegModelType : AgoraEnumerates.h
- SET_FROM : IAgoraRtcEngine.h
- setAgoraLicenseCallback() : AgoraBase.h
- setAgoraRtcEngineExternalSymbolLoader : IAgoraRtcEngine.h
- setAgoraSdkExternalSymbolLoader() : AgoraBase.h