LibJS: Move locale_relevant_extension_keys to Intl.Locale

Author: https://github.com/trflynn89
Commit: 673fc02ac5
Pull-request: https://github.com/SerenityOS/serenity/pull/9960
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Runtime/Intl/Locale.h

@@ -8,6 +8,7 @@
 
 #include <AK/Optional.h>
 #include <AK/String.h>
+#include <AK/Vector.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/Value.h>
 #include <LibUnicode/Forward.h>
@@ -20,6 +21,8 @@ class Locale final : public Object {
 public:
     static Locale* create(GlobalObject&, Unicode::LocaleID const&);
 
+    static Vector<StringView> const& relevant_extension_keys(); // [[RelevantExtensionKeys]]
+
     Locale(Object& prototype);
     Locale(Unicode::LocaleID const&, Object& prototype);
     virtual ~Locale() override = default;