Change the visibility of nav bar methods

This will help OEMs to customize the exact behavior of showing/hiding
the nav bar if they choose to extend the CarSysUI for their own
purposes.

Bug: 138242566
Test: build, manual
Change-Id: I91c76bd5d646cd356e67fe4f6900d081c6929614

packages/CarSystemUI/src/com/android/systemui/statusbar/car/CarStatusBar.java

@@ -838,7 +838,11 @@ public class CarStatusBar extends StatusBar implements CarBatteryController.Batt
         }
     }
 
-    private void attachBottomNavBarWindow() {
+    /**
+     * Attaches the bottom nav bar window. Can be extended to modify the specific behavior of
+     * attaching the bottom nav bar.
+     */
+    protected void attachBottomNavBarWindow() {
         if (!mShowBottom) {
             return;
         }
@@ -861,7 +865,11 @@ public class CarStatusBar extends StatusBar implements CarBatteryController.Batt
         mWindowManager.addView(mNavigationBarWindow, lp);
     }
 
-    private void detachBottomNavBarWindow() {
+    /**
+     * Detaches the bottom nav bar window. Can be extended to modify the specific behavior of
+     * detaching the bottom nav bar.
+     */
+    protected void detachBottomNavBarWindow() {
         if (!mShowBottom) {
             return;
         }