[Eloquent 5.7]: Provide a stable method to get the database error code

[alberthuang24]

Laravel Version: 5.7
PHP Version: 7.2.0
Database Driver & Version: mysql5.6

Description

try {
  DB::table('x')->create([
     'id' => 1
  ]);

  DB::table('x')->create([
     'id' => 1
  ]);
} catch (QueryException $e) {
  $e->getDatabaseCode();  // 1062
  $e->getCode(); // 23000 //
}

I want to support the getDatabaseCode described above