Create an alpha letter scroller

- The function used is a raised cosine function to determine the sections to animate.

Tested flag: adb shell device_config put launcher com.android.launcher3.letter_fast_scroller true
Based on recent figmaspec, size of selected letter is 28dp and regular is 20dp. That means scaling should be 28/20.
Colors are:
onSurface for letter
surfaceContainer for background.
Figma shows selected colors are materialColorOnSecondary

bug:358673724
Test manually: https://drive.google.com/file/d/1gvJd5KoK8X_Sv8jXg1cZ65R4AuqHuvcd/view?usp=sharing
Flag: com.android.launcher3.letter_fast_scroller

Change-Id: Ia86eb0e8c41bc043fda3c44aeaf59e204429f337

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

@@ -28,6 +28,7 @@ import static com.android.launcher3.logging.StatsLogManager.LauncherEvent.LAUNCH
 import static com.android.launcher3.logging.StatsLogManager.LauncherEvent.LAUNCHER_ALLAPPS_TAP_ON_WORK_TAB;
 import static com.android.launcher3.util.Executors.MAIN_EXECUTOR;
 import static com.android.launcher3.util.ScrollableLayoutManager.PREDICTIVE_BACK_MIN_SCALE;
+import static com.android.launcher3.views.RecyclerViewFastScroller.FastScrollerLocation.ALL_APPS_SCROLLER;
 
 import android.animation.Animator;
 import android.animation.AnimatorListenerAdapter;
@@ -64,6 +65,7 @@ import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.Px;
 import androidx.annotation.VisibleForTesting;
+import androidx.constraintlayout.widget.ConstraintLayout;
 import androidx.core.graphics.ColorUtils;
 import androidx.recyclerview.widget.RecyclerView;
 
@@ -167,6 +169,7 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
     protected FloatingHeaderView mHeader;
     protected View mBottomSheetBackground;
     protected RecyclerViewFastScroller mFastScroller;
+    private ConstraintLayout mFastScrollLetterLayout;
 
     /**
      * View that defines the search box. Result is rendered inside {@link #mSearchRecyclerView}.
@@ -281,6 +284,13 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
         mSearchRecyclerView = findViewById(R.id.search_results_list_view);
         mFastScroller = findViewById(R.id.fast_scroller);
         mFastScroller.setPopupView(findViewById(R.id.fast_scroller_popup));
+        mFastScrollLetterLayout = findViewById(R.id.scroll_letter_layout);
+        if (Flags.letterFastScroller()) {
+            // Set clip children to false otherwise the scroller letters will be clipped.
+            setClipChildren(false);
+        } else {
+            setClipChildren(true);
+        }
 
         mSearchContainer = inflateSearchBar();
         if (!isSearchBarFloating()) {
@@ -562,7 +572,8 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
             mActivityContext.hideKeyboard();
         }
         if (mAH.get(currentActivePage).mRecyclerView != null) {
-            mAH.get(currentActivePage).mRecyclerView.bindFastScrollbar(mFastScroller);
+            mAH.get(currentActivePage).mRecyclerView.bindFastScrollbar(mFastScroller,
+                    ALL_APPS_SCROLLER);
         }
         // Header keeps track of active recycler view to properly render header protection.
         mHeader.setActiveRV(currentActivePage);
@@ -1495,6 +1506,10 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
         }
     }
 
+    ConstraintLayout getFastScrollerLetterList() {
+        return mFastScrollLetterLayout;
+    }
+
     /**
      * redraws header protection
      */
@@ -1562,7 +1577,7 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
         void setup(@NonNull View rv, @Nullable Predicate<ItemInfo> matcher) {
             mAppsList.updateItemFilter(matcher);
             mRecyclerView = (AllAppsRecyclerView) rv;
-            mRecyclerView.bindFastScrollbar(mFastScroller);
+            mRecyclerView.bindFastScrollbar(mFastScroller, ALL_APPS_SCROLLER);
             mRecyclerView.setEdgeEffectFactory(createEdgeEffectFactory());
             mRecyclerView.setApps(mAppsList);
             mRecyclerView.setLayoutManager(mLayoutManager);