[fuzzer] Adds code generation target.

[coder7695]

The code generation fuzzer target helped identify issue #8793 in TsCodeGenerator.

The PR solves the TSCodeGenerator issue by using parser_.empty_namespace_ in the GenerateEntry() method of idl_gen_ts.cpp.
The destructor of Parser class handles object deletion and also handle empty_namespace deletion which is added to the namespaces_ collection.

  ~Parser() {
    for (auto it = namespaces_.begin(); it != namespaces_.end(); ++it) {
      delete *it;
    }
  }

The PR also adds code generation fuzzer target to fuzz code generation for various languages. Also implements TODO items in the parser fuzzer.