yuzu qt: Add an Apply button to configuration dialogs

Most of the code already exists to do this, but the Apply button itself
was never added. This adds a button and boolean that tells yuzu to save
the configuration after applying settings, even if close/Cancel is
pressed on the dialog. Changes after applying will not be saved when
Cancel is pressed, though.

src/yuzu/uisettings.h

@@ -95,6 +95,8 @@ struct Values {
     uint8_t row_2_text_id;
     std::atomic_bool is_game_list_reload_pending{false};
     bool cache_game_list;
+
+    bool configuration_applied;
 };
 
 extern Values values;