Revert "No NavigationBar layer in tablets"

This reverts commit fb999dc720.

Reason for revert: breaking TaplTestsLauncher3.testDevicePressMenu and testPressHomeOnAllAppsContextMenu for all foldable targetse

Bug: 191660313
Change-Id: I04c9e28c92ed0cf9e822ecf4409edfc8f37c36c4

packages/SystemUI/src/com/android/systemui/navigationbar/NavigationBarController.java

@@ -251,7 +251,8 @@ public class NavigationBarController implements Callbacks,
 
     /** @return {@code true} if taskbar is enabled, false otherwise */
     private boolean initializeTaskbarIfNecessary() {
-        if (mIsTablet) {
+        boolean isShowingTaskbar = mIsTablet && mNavMode == NAV_BAR_MODE_3BUTTON;
+        if (isShowingTaskbar) {
             // Remove navigation bar when taskbar is showing, currently only for 3 button mode
             removeNavigationBar(mContext.getDisplayId());
             mCommandQueue.addCallback(mTaskbarDelegate);
@@ -260,7 +261,7 @@ public class NavigationBarController implements Callbacks,
             mCommandQueue.removeCallback(mTaskbarDelegate);
             mTaskbarDelegate.destroy();
         }
-        return mIsTablet;
+        return isShowingTaskbar;
     }
 
     @Override
@@ -331,7 +332,7 @@ public class NavigationBarController implements Callbacks,
             return;
         }
 
-        if (mIsTablet) {
+        if (mIsTablet && mNavMode == NAV_BAR_MODE_3BUTTON) {
             return;
         }