Enhanced broadcasting new API

[aleksandr-voitenko]

Description

This code allows Enhanced Broadcasting to be used with the new back-end API.
At first I was trying to implement it as a simple Boolean flag in the settings, but soon realized that dual output mode would be near impossible to implement this way, so I came up to a new design.

export interface IEnhancedBroadcastingAdvancedStreaming extends IAdvancedStreaming {
    // If set, the Enhanced Broadcasting stream will be in the Dual Output mode.
    // This value should be initialized before the stream start.
    additionalVideo?: IVideo,
}
export interface IEnhancedBroadcastingAdvancedStreamingFactory {
    create(): IEnhancedBroadcastingAdvancedStreaming;
    destroy(stream: IEnhancedBroadcastingAdvancedStreaming): void;
    legacySettings: IEnhancedBroadcastingAdvancedStreaming;
}

Essentially, in the example above you see AdvancedStreaming enhanced by the optional canvas.

Interface of Streaming has also changes slightly. Now presence of an encoder is optional.

export interface IStreaming {
    // Video encoder value is ignored in the Enhanced Broadcasting mode
    videoEncoder?: IVideoEncoder;
    ...

Why this design?

Mainly because of the Twitch Dual Streaming mode that requires vertical and horizontal videos to be streamed to a single endpoint.

On top of that

I refactored and generalized code related to streaming. Additionally, improved encapsulation of several classes.
I refactored existing Enhanced Broadcasting code to support both new and old (OBS_service) APIs. As a result, backward compatibility is enabled.

And finally

Error handling has been improved, especially during stream start.

How Has This Been Tested?

Manually and via unit tests. Windows only.

Types of changes

• New feature (non-breaking change which adds functionality) -->