Correct the page scrolls of the AddDesktopButton

Do not apply the button's grid translation to its page scrolls if
it is not showing as a grid,otherwise the `mCurrentPage` may not be
set correctly while checking `ensureWithinScrollBounds`.

Bug: 396146789
Flag: com.android.window.flags.enable_multiple_desktops_frontend
Flag: com.android.window.flags.enable_multiple_desktops_backend
Test: m
Change-Id: Ia1378a997e681abda60fa1cb3c125660916df4c5

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

@@ -6243,8 +6243,8 @@ public abstract class RecentsView<
         int addDesktopButtonIndex = indexOfChild(mAddDesktopButton);
         if (addDesktopButtonIndex != -1 && addDesktopButtonIndex < outPageScrolls.length) {
             outPageScrolls[addDesktopButtonIndex] =
-                    newPageScrolls[addDesktopButtonIndex] + Math.round(
-                            mAddDesktopButton.getGridTranslationX());
+                    newPageScrolls[addDesktopButtonIndex] + mAddDesktopButton.getScrollAdjustment(
+                            showAsGrid);
         }
 
         int lastTaskScroll = getLastTaskScroll(clearAllScroll, clearAllWidth);