Add taskbar stashing feedforward, i.e. hint at upcoming stash/unstash

Also fix unstashing not working in 3P launchers by moving the unstash call from LauncherTaskbarUIController to TaskbarActivityContext

Test: long press taskbar background and stashed handle, watch it hint towards the new stashed/unstashed state respectively and then complete the animation when the long press is triggered
Fixes: 193926311
Fixes: 192926350
Change-Id: I0e538be9129bf5c600d07f360b8106d7077862ad

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

@@ -40,6 +40,8 @@ public class StashedHandleViewController {
     private final int mStashedHandleHeight;
     private final AnimatedFloat mTaskbarStashedHandleAlpha = new AnimatedFloat(
             this::updateStashedHandleAlpha);
+    private final AnimatedFloat mTaskbarStashedHandleHintScale = new AnimatedFloat(
+            this::updateStashedHandleHintScale);
 
     // Initialized in init.
     private TaskbarControllers mControllers;
@@ -64,6 +66,7 @@ public class StashedHandleViewController {
         mStashedHandleView.getLayoutParams().height = mActivity.getDeviceProfile().taskbarSize;
 
         updateStashedHandleAlpha();
+        mTaskbarStashedHandleHintScale.updateValue(1f);
 
         final int stashedTaskbarHeight = mControllers.taskbarStashController.getStashedHeight();
         mStashedHandleView.setOutlineProvider(new ViewOutlineProvider() {
@@ -80,12 +83,24 @@ public class StashedHandleViewController {
                 outline.setRoundRect(mStashedHandleBounds, mStashedHandleRadius);
             }
         });
+
+        mStashedHandleView.addOnLayoutChangeListener((view, i, i1, i2, i3, i4, i5, i6, i7) -> {
+            final int stashedCenterX = view.getWidth() / 2;
+            final int stashedCenterY = view.getHeight() - stashedTaskbarHeight / 2;
+
+            view.setPivotX(stashedCenterX);
+            view.setPivotY(stashedCenterY);
+        });
     }
 
     public AnimatedFloat getStashedHandleAlpha() {
         return mTaskbarStashedHandleAlpha;
     }
 
+    public AnimatedFloat getStashedHandleHintScale() {
+        return mTaskbarStashedHandleHintScale;
+    }
+
     /**
      * Creates and returns a {@link RevealOutlineAnimation} Animator that updates the stashed handle
      * shape and size. When stashed, the shape is a thin rounded pill. When unstashed, the shape
@@ -105,4 +120,9 @@ public class StashedHandleViewController {
     protected void updateStashedHandleAlpha() {
         mStashedHandleView.setAlpha(mTaskbarStashedHandleAlpha.value);
     }
+
+    protected void updateStashedHandleHintScale() {
+        mStashedHandleView.setScaleX(mTaskbarStashedHandleHintScale.value);
+        mStashedHandleView.setScaleY(mTaskbarStashedHandleHintScale.value);
+    }
 }