FS-7513: refactor conference video muxing to create one distinct encoder per codec used and only create one encoded frame per distinct codec, store current image used by layer on the layer so it is not destroyed before the canvas is written, refactor and rearrange some functions

FS-7513: fix compiler warning about uninitialized var and make sure allocated memory is filled with 0

FS-7513: refactor mcu code, put everyone on a canvas and send out using a dedicated thread with a constant FPS

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FS-7166 #resolve

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revert