Refactor some codes for unbundle

1. Move some @hide codes to DocumentsUI itself utils files.
2. Refactor some @hide api call to normal api call
   for same function
3. Remove unnecessary @hide api call.

Bug: 118794189
Bug: 118271458
Test: atest DocumentsUITests
Change-Id: I319ee2149d7594e20287638037739cc5ee4b0554
diff --git a/src/com/android/documentsui/ShortcutsUpdater.java b/src/com/android/documentsui/ShortcutsUpdater.java
index c4269f3..258f71e 100644
--- a/src/com/android/documentsui/ShortcutsUpdater.java
+++ b/src/com/android/documentsui/ShortcutsUpdater.java
@@ -117,7 +117,7 @@
     }
 
     private int getNumDynSlots(ShortcutManager mgr, int numDevices) {
-        int slots = mgr.getMaxShortcutCountForActivity() - mgr.getManifestShortcuts().size();
+        int slots = mgr.getMaxShortcutCountPerActivity() - mgr.getManifestShortcuts().size();
         return numDevices >= slots ? slots : numDevices;
     }