Add a header container view to the widgets full sheet

A header container view will contain
1. A horizontal bar: for indicating the popup view can be dragged
   to dismiss:
2. A title view: a title of the widgets full sheet popup view.
3. A search bar: for widgets / shortcut search. Since we will be
   making the fallback search algorithm available in AOSP, the
   search bar will now live in the Launcher3 codebase.
4. Recommended widgets (coming soon...)

This CL also added a scroll effect which gradually collapses the
title view when the user scrolls down the recycler view. The title
view will gradually restore its height when the user scroll to the
top of the recycler view.

Test: Manually test widgets pickers in work profile and non work
      profile setup. Verified the fast scroll bar works well in
      both setup.
      With searchbar: https://drive.google.com/file/d/19grUHL_LspLhMD_5p6-i0CiMW1FpflmD/view?usp=sharing
      Without searchbar: https://drive.google.com/file/d/1KRPgEAESHUhJDo1UJsQN80JO1c9Y8Nhl/view?usp=sharing

Bug: 179797520

Change-Id: If0016e3b3c693414897140e7912531ed9bd5deef

src/com/android/launcher3/BaseRecyclerView.java

@@ -23,6 +23,7 @@ import android.view.View;
 import android.view.ViewGroup;
 import android.view.accessibility.AccessibilityNodeInfo;
 
+import androidx.recyclerview.widget.LinearLayoutManager;
 import androidx.recyclerview.widget.RecyclerView;
 
 import com.android.launcher3.compat.AccessibilityManagerCompat;
@@ -188,4 +189,21 @@ public abstract class BaseRecyclerView extends RecyclerView  {
         super.onInitializeAccessibilityNodeInfo(info);
         if (isLayoutSuppressed()) info.setScrollable(false);
     }
+
+    /**
+     * Scrolls this recycler view to the top.
+     */
+    public void scrollToTop() {
+        if (mScrollbar != null) {
+            mScrollbar.reattachThumbToScroll();
+        }
+        if (getLayoutManager() instanceof LinearLayoutManager) {
+            LinearLayoutManager layoutManager = (LinearLayoutManager) getLayoutManager();
+            if (layoutManager.findFirstCompletelyVisibleItemPosition() == 0) {
+                // We are at the top, so don't scrollToPosition (would cause unnecessary relayout).
+                return;
+            }
+        }
+        scrollToPosition(0);
+    }
 }