Fix 3-button Navigation Switch Access Long press

This cl includes
 - Make long press of back navigation button of 3 button navigation mode behave just like short press.

Test: Manual
Bug: 315723734
Flag: EXEMPT bugfix
Change-Id: Id897c84dcb33f73174ea907c5ab5655d2ac5ba10

quickstep/src/com/android/launcher3/taskbar/TaskbarNavButtonController.java

@@ -281,6 +281,10 @@ public class TaskbarNavButtonController implements TaskbarControllers.LoggableTa
     }
 
     private void resetScreenUnpin() {
+        // if only back button was long pressed, navigate back like a single click back behavior.
+        if (mLongPressedButtons == BUTTON_BACK) {
+            executeBack(null);
+        }
         mLongPressedButtons = 0;
         mLastScreenPinLongPress = 0;
     }