feat: add option to disable desktop sharing

config.disableDesktopSharing - when set to false will disable desktop
sharing

interfaceConfig.DESKTOP_SHARING_BUTTON_DISABLED_TOOLTIP - when value is
assigned, will not hide the desktop sharing button completely, but show
as disabled with this value used as the tooltip text.

react/features/toolbox/functions.web.js

@@ -43,6 +43,10 @@ export function getButtonAttributesByProps(props: Object = {})
         result.style = { display: 'none' };
     }
 
+    if (props.tooltipText) {
+        result.content = props.tooltipText;
+    }
+
     return result;
 }