Add title and icon in panel header

- Add getIcon() and getSubTitle() in PanelContent
- Check icon avalibility to decide header layout
- Add test cases

Bug: 147776885
Test: make -j42 RunSettingsRoboTests
Change-Id: Idb51e81359b6037ca9b90965dd9b370fc5e22c84

src/com/android/settings/panel/PanelContent.java

@@ -28,6 +28,20 @@ import java.util.List;
  */
 public interface PanelContent extends Instrumentable {
 
+    /**
+     * @return a icon resource for the title of the Panel.
+     */
+    default int getIcon() {
+        return -1;
+    }
+
+    /**
+     * @return a string for the subtitle of the Panel.
+     */
+    default CharSequence getSubTitle() {
+        return null;
+    }
+
     /**
      * @return a string for the title of the Panel.
      */