Userland: Prefer _short_string over String::from_utf8_short_string

This user-defined literal is a strictly equivalent but shorter alias to
`String::from_utf8_short_string`.

Userland/Utilities/netstat.cpp

@@ -138,7 +138,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
 
     auto get_formatted_user = [&](i32 uid) -> ErrorOr<String> {
         if (uid == -1)
-            return String::from_utf8_short_string("-"sv);
+            return "-"_short_string;
 
         return String::number(uid);
     };