Bug 1755961 - Delete the format cache in AppDateTimeFormat; r=platform-i18n-reviewers,dminor

Differential Revision: https://phabricator.services.mozilla.com/D142470

intl/locale/AppDateTimeFormat.cpp

@@ -255,6 +255,7 @@ void AppDateTimeFormat::Shutdown() {
 /*static*/
 void AppDateTimeFormat::ClearLocaleCache() {
   MOZ_ASSERT(NS_IsMainThread());
+  DeleteCache();
   delete sLocale;
   sLocale = nullptr;
 }