Support for animating A-Z <-> Search.

Demo videos (1/5 speed) and APK: https://drive.google.com/drive/folders/1qQNzcoibiFMzxYhvXc7UEHCaBhJg6SjN?resourcekey=0-OWD06iLXg3wf_eWce4rUPA&usp=sharing

Bug: 234882587
Bug: 243688989
Test: Manually tested a bunch of cases at 1/10 animation speed.
Such as work profile or not, suggested apps enabled/disabled,
typing during the animation, going back during the animation,
web results injected above apps, etc.

Change-Id: Id4f1a858d387bf3a7f9cf2d23564a276544abef1

src/com/android/launcher3/allapps/BaseAllAppsAdapter.java

@@ -127,6 +127,11 @@ public abstract class BaseAllAppsAdapter<T extends Context & ActivityContext> ex
         public boolean isContentSame(AdapterItem other) {
             return itemInfo == null && other.itemInfo == null;
         }
+
+        /** Sets the alpha of the decorator for this item. Returns true if successful. */
+        public boolean setDecorationFillAlpha(int alpha) {
+            return false;
+        }
     }
 
     protected final T mActivityContext;