[PATCH v2 0/6] MR4195: winegstreamer: Introduce some helper functions and implement add_stream.

[Ziqing Hui (＠zhui)]

This MR is splitted from !3810

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  v2: winegstreamer: Implement wg_muxer_add_stream.
      winegstreamer: Introduce factory_create_element.
      winegstreamer: Introduce find_element_factories.

https://gitlab.winehq.org/wine/wine/-/merge_requests/4195