fix(preferences): fragment back stack being reset

the backPressed callbacks are disabled when the fragment is created, and get enabled when the backstack changes with the backstack listeners

The issue was that after an activity recreation, the callbacks weren't being enabled because there was no backstack change

So, enabling them manually when the view is created fix that

(cherry picked from commit 235e376)

Author: BrayanDSO

AnkiDroid/src/main/java/com/ichi2/anki/preferences/Preferences.kt

@@ -161,6 +161,9 @@ class PreferencesFragment :
 
         parentFragmentManager.addOnBackStackChangedListener(parentBackStackListener)
         childFragmentManager.addOnBackStackChangedListener(childBackStackListener)
+
+        childFragmentOnBackPressedCallback.isEnabled = !settingsIsSplit && childFragmentManager.backStackEntryCount > 0
+        parentFragmentOnBackPressedCallback.isEnabled = parentFragmentManager.backStackEntryCount > 0
     }
 
     private fun setFragmentTitleOnToolbar(fragment: Fragment) {