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/configuration/configure_per_game.h

@@ -39,6 +39,8 @@ private:
     void changeEvent(QEvent* event) override;
     void RetranslateUI();
 
+    void HandleApplyButtonClicked();
+
     void LoadConfiguration();
 
     std::unique_ptr<Ui::ConfigurePerGame> ui;