【owtnativeclient】桌面共享流

• owt默认支持 桌面共享类型的 localstream 添加
• 支持多个localstream的发布。
• videotrack的source看起来是owt 封装实现的
• audiotrack的source 是webrtc自己的

owt 桌面共享stream

/**@brief Initialize a local screen stream with parameters.@param parameters Parameters for creating the stream. The stream willnot be impacted if changing parameters after it is created.@param observer Source callback required for application to specify capturewindow/screen source.@return Pointer to created LocalStream.*/static std::shared_ptr<LocalStream> Create(std