Makes Settings > Accessibility > Magnification prefs searchable.

All preferences are searchable except for "Keep on while switching apps"
which is only searchable if the user already has a magnification
shortcut enabled, to minimize user confusion from that generically-named
preference.

NO_IFTTT=adding IFTTT

Fix: 353772926
Test: atest ToggleScreenMagnificationPreferenceFragmentTest
Flag: com.android.settings.accessibility.fix_a11y_settings_search
Test: adb shell pm clear com.google.android.settings.intelligence;
      search Settings for the items in the bug
Change-Id: I01c7e5586ec0ea432cb2df80f156141683b97522