CoreText: Get user's preferred languages via NSLocale instead of NSUserDefaults

The latter API is considered a potential privacy risk, and needs
explicit declaration of use for iOS in the privacy manifest, so
avoid it if we can, to simplify things.

Task-number: QTBUG-114319
Pick-to: 6.7
Change-Id: Ica6fef47720696bc9ab25cb25642d6650f618b70
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Doris Verria <doris.verria@qt.io>

src/gui/text/coretext/qcoretextfontdatabase.mm

@@ -572,7 +572,7 @@ CFArrayRef fallbacksForDescriptor(CTFontDescriptorRef descriptor)
     }
 
     CFArrayRef cascadeList = CFArrayRef(CTFontCopyDefaultCascadeListForLanguages(font,
-        (CFArrayRef)[NSUserDefaults.standardUserDefaults stringArrayForKey:@"AppleLanguages"]));
+        (CFArrayRef)NSLocale.preferredLanguages));
 
     if (!cascadeList) {
         qCWarning(lcQpaFonts) << "Failed to create fallback cascade list for" << descriptor;