Encode a password during mapping in forMember()

To encode a password in symfony, we have to use `UserPasswordEncoderInterface` to encode the password. It will need to pass the User entity as first parameter for the method `encodePassword()`.

It will be cool if we could do something like

```
$config->registerMapping(UserDto::class, User::class)
->forMember("password", function($source, $destination) use ($passwordEncoder) {
return $passwordEncoder->encodePassword($destination, $source->password);
});
```

Start by locating the implementation of registerMapping() and forMember(), then inspect how the mapping callback receives the source and destination objects. Done means a forMember() callback can pass the destination User entity and source password to UserPasswordEncoderInterface::encodePassword().

Written by the indexing model from the issue text.