Fix the bottom action bar non-functional

For the latest version of AndroidX Fragments, the fragments' lifecycle change when switching the fragment by calling FragmentTransaction#replace().
It causes the bottom action bar non-functional.
We need to change our logic to fulfill the new behavior of Fragments.

Bug: 166304794
Change-Id: I313e248fcd8012b20741b3aaec7d36d43736a6d5
diff --git a/src/com/android/wallpaper/picker/CategorySelectorFragment.java b/src/com/android/wallpaper/picker/CategorySelectorFragment.java
index 887eb92..957b227 100644
--- a/src/com/android/wallpaper/picker/CategorySelectorFragment.java
+++ b/src/com/android/wallpaper/picker/CategorySelectorFragment.java
@@ -94,6 +94,11 @@
          * Fetches the wallpaper categories.
          */
         void fetchCategories();
+
+        /**
+         * Hides the {@link com.android.wallpaper.widget.BottomActionBar}.
+         */
+        void hideBottomActionBar();
     }
 
     private RecyclerView mImageGrid;
@@ -131,6 +136,8 @@
             getCategorySelectorFragmentHost().fetchCategories();
         }
 
+        getCategorySelectorFragmentHost().hideBottomActionBar();
+
         return view;
     }