feat(virtual-background): Desktop share as virtual background

react/features/stream-effects/virtual-background/JitsiStreamBackgroundEffect.js

             this._outputCanvasCtx.drawImage(
                 this._virtualVideo,
                 0,
-                0
+                0,
+                this._inputVideoElement.width,
+                this._inputVideoElement.height
             );
         } else {
             this._outputCanvasCtx.filter = `blur(${this._options.virtualBackground.blurValue}px)`;

react/features/virtual-background/middleware.js

+// @flow
+
 import { JitsiTrackEvents } from '../base/lib-jitsi-meet';
 import { MiddlewareRegistry } from '../base/redux';
 import { getLocalVideoTrack } from '../base/tracks';