Fix rebuild being triggered on every menu open()

Fixes #7924

JRE 8u161 made JMenu.insert() MUCH slower on OSX.
This exposed a bug lurking there for years; in fact the menu entries were rebuilt every time since JMenu.getComponent() returns an empty list.
The correct function is JMenu.getMenuComponents().
In the meantime, also remove sketchbookMenu and examplesMenu being deleted on board change; only their content needs to be updated, not the container itself.

Author: facchinm

app/src/processing/app/Editor.java

@@ -262,8 +262,6 @@ public void windowActivated(WindowEvent e) {
         // added for 1.0.5
         // http://dev.processing.org/bugs/show_bug.cgi?id=1260
         public void windowDeactivated(WindowEvent e) {
-          fileMenu.remove(sketchbookMenu);
-          fileMenu.remove(examplesMenu);
           List<Component> toolsMenuItemsToRemove = new LinkedList<>();
           for (Component menuItem : toolsMenu.getMenuComponents()) {
             if (menuItem instanceof JComponent) {
@@ -504,7 +502,7 @@ private void buildMenuBar() {
     fileMenu.addMenuListener(new StubMenuListener() {
       @Override
       public void menuSelected(MenuEvent e) {
-        List<Component> components = Arrays.asList(fileMenu.getComponents());
+        List<Component> components = Arrays.asList(fileMenu.getMenuComponents());
         if (!components.contains(sketchbookMenu)) {
           fileMenu.insert(sketchbookMenu, 3);
         }
@@ -537,7 +535,7 @@ public void menuSelected(MenuEvent e) {
     toolsMenu.addMenuListener(new StubMenuListener() {
       @Override
       public void menuSelected(MenuEvent e) {
-        List<Component> components = Arrays.asList(toolsMenu.getComponents());
+        List<Component> components = Arrays.asList(toolsMenu.getMenuComponents());
         int offset = 0;
         for (JMenu menu : base.getBoardsCustomMenus()) {
           if (!components.contains(menu)) {