Speed up BasePreferenceController.updateNonIndexableKeys

By avoid unnecessary calls to getAvailabilityStatus(), which also avoid
unnecessary crash potential.
- When key already marked searchable="false" in xml, no need to check
  getAvailabilityStatus() again.
- When getAvailabilityStatus() return AVAILABLE, no need to call it
  again to check it not equals to AVAILABLE_UNSEARCHABLE.

Bug: 352455031
Flag: EXEMPT refactor
Test: redo search index - by changing locale
Change-Id: Ic0c43b9bcd5974907b3a7d4aba73d4c7203f8af4