Handle visibility of AddDesktopButton for overview/quickswitch

This change introduces mDisallowScrollToAddDesk to handle the visibility
of AddDesktopButton in overview/quickswitch. In overview, set its scroll
as the first task; in quick switch, set its scroll out range of
[minScroll, maxScroll].

Bug: 398036110
Flag: com.android.window.flags.enable_multiple_desktops_frontend
Flag: com.android.window.flags.enable_multiple_desktops_backend
Test: manual quick switch
Change-Id: I5fada0c4c5bccc5572b458da9970e3524087508d

quickstep/src/com/android/quickstep/views/RecentsView.java

@@ -586,6 +586,8 @@ public abstract class RecentsView<
     private final TaskOverlayFactory mTaskOverlayFactory;
 
     protected boolean mDisallowScrollToClearAll;
+    // True if it is not allowed to scroll to [AddDesktopButton].
+    protected boolean mDisallowScrollToAddDesk;
     private boolean mOverlayEnabled;
     protected boolean mFreezeViewVisibility;
     private boolean mOverviewGridEnabled;
@@ -6164,6 +6166,17 @@ public abstract class RecentsView<
             updateMinAndMaxScrollX();
         }
     }
+    /**
+     * Update the value of [mDisallowScrollToAddDesk]
+     */
+    public void setDisallowScrollToAddDesk(boolean disallowScrollToAddDesk) {
+        if (mDisallowScrollToAddDesk != disallowScrollToAddDesk) {
+            mDisallowScrollToAddDesk = disallowScrollToAddDesk;
+            updateMinAndMaxScrollX();
+        }
+    }
+
+
 
     /**
      * Updates page scroll synchronously after measure and layout child views.
@@ -6309,7 +6322,20 @@ public abstract class RecentsView<
         if (addDesktopButtonIndex >= 0 && addDesktopButtonIndex < outPageScrolls.length) {
             int firstViewIndex = getFirstViewIndex();
             if (firstViewIndex >= 0 && firstViewIndex < outPageScrolls.length) {
-                outPageScrolls[addDesktopButtonIndex] = outPageScrolls[firstViewIndex];
+                // If we can scroll to [AddDesktopButton], make its page scroll equal to
+                // the first [TaskView]. Otherwise, make its page scroll out of range of
+                // [minScroll, maxScroll].
+                if (!mDisallowScrollToAddDesk) {
+                    outPageScrolls[addDesktopButtonIndex] = outPageScrolls[firstViewIndex];
+                } else {
+                    outPageScrolls[addDesktopButtonIndex] =
+                            outPageScrolls[firstViewIndex] + (mIsRtl ? 1 : -1);
+                }
+            }
+
+            if (DEBUG) {
+                Log.d(TAG, "getPageScrolls - addDesktopButtonScroll: "
+                        + outPageScrolls[addDesktopButtonIndex]);
             }
         }
         if (DEBUG) {