Add a default implementation of strength

This is too simple to be useful, but its a start.

gtk/gtkpasswordentry.c

@@ -558,10 +558,17 @@ update_strength (GObject          *object,
 {
   GtkPasswordEntryPrivate *priv = gtk_password_entry_get_instance_private (entry);
 
-  int strength = 0;
+  int strength = -1;
 
   g_signal_emit (entry, signals[GET_STRENGTH], 0, &strength);
 
+  if (strength == -1)
+    {
+      const char *text = gtk_editable_get_text (GTK_EDITABLE (priv->entry));
+
+      strength = CLAMP (0, 100, 10 * g_utf8_strlen (text, -1));
+    }
+
   gtk_level_bar_set_value (GTK_LEVEL_BAR (priv->strength_widget), strength);
 }