Demo: Make content pane wrapping opt-in

For now we should only delegate the creation of the content pane to the BaseComponentDemo for demos which explicitly support the Spec declarations.

core/src/test/java/com/github/weisj/darklaf/ui/button/AbstractButtonDemo.java

@@ -82,6 +82,11 @@ public abstract class AbstractButtonDemo<T extends AbstractButton> extends BaseC
         enumSpecWithNone(DarkButtonUI.KEY_CORNER, AlignmentExt.class);
     }
 
+    @Override
+    protected boolean supportsSpec() {
+        return true;
+    }
+
     protected void initBaseControls() {}
 
     protected abstract T createButton();

core/src/test/java/com/github/weisj/darklaf/ui/demo/BaseComponentDemo.java

@@ -43,7 +43,7 @@ public abstract class BaseComponentDemo implements ComponentDemo, DemoExecutionS
     @Override
     public JComponent getContentPane() {
         JComponent component = getComponent();
-        if (component instanceof DemoPanel) return component;
+        if (!supportsSpec()) return component;
         init();
 
         DemoPanel demoPanel = new DemoPanel(component);
@@ -156,6 +156,10 @@ public abstract class BaseComponentDemo implements ComponentDemo, DemoExecutionS
         addSpec(new SpacerSpec());
     }
 
+    protected boolean supportsSpec() {
+        return false;
+    }
+
     @Override
     public List<DemoSpec<?>> getSpecs() {
         return demoSpecList.stream()