video-split: rounded corners in active participant

Change-Id: I4176e7ea772c3471f153f8069958566ddcf0c384

src/mainview/components/ParticipantOverlay.qml

@@ -120,7 +120,10 @@ Item {
         overlayItems: Rectangle {
             id: overlayRect
 
-            anchors.fill: parent
+            width: participantIsActive ? mediaDistRender.contentRect.width : undefined
+            height: participantIsActive ? mediaDistRender.contentRect.height : undefined
+            anchors.centerIn: participantIsActive ? parent : undefined
+            anchors.fill: participantIsActive ? undefined : parent
             color: "transparent"
 
             Item {