Adds initial Taskbar Edu implementation.

Currently it just pops up with one placeholder image for splitscreen.
The Next button doesn't do anything.

Screenshots:
Light: https://screenshot.googleplex.com/B27CwBcwobHTghN.png
Dark: https://screenshot.googleplex.com/48EuJZv8evd5RGW.png

Known issues:
 - Back gesture is picked up behind by the app behind the taskbar.
 - When the flag is enabled, the Edu shows up each time you open
   an app, rather than only the first time.

Bug: 180605356
Test: Manual
Change-Id: Ifba9aa59abf1501b5f8ddebb3fcc13df85f6efaa

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

@@ -34,6 +34,7 @@ public class TaskbarControllers {
     public final TaskbarKeyguardController taskbarKeyguardController;
     public final StashedHandleViewController stashedHandleViewController;
     public final TaskbarStashController taskbarStashController;
+    public final TaskbarEduController taskbarEduController;
 
     /** Do not store this controller, as it may change at runtime. */
     @NonNull public TaskbarUIController uiController = TaskbarUIController.DEFAULT;
@@ -47,7 +48,8 @@ public class TaskbarControllers {
             TaskbarViewController taskbarViewController,
             TaskbarKeyguardController taskbarKeyguardController,
             StashedHandleViewController stashedHandleViewController,
-            TaskbarStashController taskbarStashController) {
+            TaskbarStashController taskbarStashController,
+            TaskbarEduController taskbarEduController) {
         this.taskbarActivityContext = taskbarActivityContext;
         this.taskbarDragController = taskbarDragController;
         this.navButtonController = navButtonController;
@@ -58,6 +60,7 @@ public class TaskbarControllers {
         this.taskbarKeyguardController = taskbarKeyguardController;
         this.stashedHandleViewController = stashedHandleViewController;
         this.taskbarStashController = taskbarStashController;
+        this.taskbarEduController = taskbarEduController;
     }
 
     /**