LibJS: Implement Temporal.Now.plainDateTime()

Author: https://github.com/linusg
Commit: 0bb19fc51c
Pull-request: https://github.com/SerenityOS/serenity/pull/9031
Reviewed-by: https://github.com/IdanHo ✅

Userland/Libraries/LibJS/Runtime/Temporal/Now.h

@@ -21,6 +21,7 @@ public:
 private:
     JS_DECLARE_NATIVE_FUNCTION(time_zone);
     JS_DECLARE_NATIVE_FUNCTION(instant);
+    JS_DECLARE_NATIVE_FUNCTION(plain_date_time);
     JS_DECLARE_NATIVE_FUNCTION(plain_date);
     JS_DECLARE_NATIVE_FUNCTION(plain_date_iso);
 };