Fix back button touch region too small

The back button in 3-button-nav touch region was unintentionally
decreased with the predictive_back_three_button_nav flag. The reason is
that NearestTouchFrame did not consider the back button for its touch
forwarding logic, because the back button did not have isClickable set
to true. Manually setting the clickable attribute fixes that.

Bug: 393498908
Test: Manual, i.e. verified that touches close to back button are not routed to the home button
Flag: EXEMPT bugfix
Change-Id: I7ad1ee13f92aa947f1a86f8d65de79a9d9e13899

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

@@ -870,6 +870,9 @@ public class NavbarButtonsViewController implements TaskbarControllers.LoggableT
         if (predictiveBackThreeButtonNav() && buttonType == BUTTON_BACK) {
             // set up special touch listener for back button to support predictive back
             setBackButtonTouchListener(buttonView, navButtonController);
+            // Set this View clickable, so that NearestTouchFrame.java forwards closeby touches to
+            // this View
+            buttonView.setClickable(true);
         } else {
             buttonView.setOnClickListener(view ->
                     navButtonController.onButtonClick(buttonType, view));