Initial commit of taskbar stashing

- Added StashedHandleViewController to provide properties such as ViewOutlineProvider to animate the handle that's shown in place of taskbar while it's stashed
- Added TaskbarStashController to coordinate the stashed state, including orchestrating the animation across taskbar controllers
- Added TaskbarStashInput consumer to detect long press in the nav region when taskbar is stashed

Behavior:
- Long pressing taskbar background animates to the stashed state by morphing the TaskbarView into the stashed handle view and offsetting the background offscreen
- We persist the stashed state across app launches and reboot; to unstash, long press the stashed handle
- We also visually unstash when going back home

Test: long press tasbkar background when in an app to stash it, long press the resulting stashed handle to unstash; while stashed, swipe up to home to also unstash until launching another app
Bug: 189503603
Change-Id: I698eff785388dff1ef717c76879719d6af236c2d

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

@@ -39,6 +39,8 @@ public class TaskbarDragLayerController {
     // Alpha properties for taskbar background.
     private final AnimatedFloat mBgTaskbar = new AnimatedFloat(this::updateBackgroundAlpha);
     private final AnimatedFloat mBgNavbar = new AnimatedFloat(this::updateBackgroundAlpha);
+    // Translation property for taskbar background.
+    private final AnimatedFloat mBgOffset = new AnimatedFloat(this::updateBackgroundOffset);
 
     // Initialized in init.
     private TaskbarControllers mControllers;
@@ -78,10 +80,18 @@ public class TaskbarDragLayerController {
         return mBgNavbar;
     }
 
+    public AnimatedFloat getTaskbarBackgroundOffset() {
+        return mBgOffset;
+    }
+
     private void updateBackgroundAlpha() {
         mTaskbarDragLayer.setTaskbarBackgroundAlpha(Math.max(mBgNavbar.value, mBgTaskbar.value));
     }
 
+    private void updateBackgroundOffset() {
+        mTaskbarDragLayer.setTaskbarBackgroundOffset(mBgOffset.value);
+    }
+
     /**
      * Callbacks for {@link TaskbarDragLayer} to interact with its controller.
      */