Provide "Restart Now" functionality

And use it for the plugin dialog and when changing the UI language.

Change-Id: Ic767837d2526409f7ec46d7e4612a1499f19459e
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/libs/extensionsystem/pluginmanager.cpp

@@ -536,6 +536,17 @@ QStringList PluginManager::arguments()
     return d->arguments;
 }
 
+/*!
+    The arguments that should be used when automatically restarting the application.
+    This includes plugin manager related options for enabling or disabling plugins,
+    but excludes others, like the arguments returned by arguments() and the appOptions
+    passed to the parseOptions() method.
+*/
+QStringList PluginManager::argumentsForRestart()
+{
+    return d->argumentsForRestart;
+}
+
 /*!
     List of all plugin specifications that have been found in the plugin search paths.
     This list is valid directly after the setPluginPaths() call.