LibPDF: Extract reference bitpacking into dedicated class

Author: https://github.com/BenWiederhake
Commit: d344253b08
Pull-request: https://github.com/SerenityOS/serenity/pull/10080
Reviewed-by: https://github.com/alimpfard

Userland/Libraries/LibPDF/Parser.cpp

@@ -660,7 +660,7 @@ Value Parser::parse_possible_indirect_value_or_ref()
         m_reader.discard();
         consume();
         consume_whitespace();
-        return Value(first_number.as_int(), second_number.as_int());
+        return Value(Reference(first_number.as_int(), second_number.as_int()));
     }
 
     if (m_reader.matches("obj")) {