Add a possibility to have custom dependencies in Custom Transformer

[06romix]

What do you think about adding a possibility to have custom dependencies in Custom Transformer? We can allow passing the already created object of Transformer into configuration instead of the class name.

Developing the AMP plugin for Magento 2, I have to use a service similar to Psr\Container\ContainerInterface to support dependency inversion. And it would be nice to have an opportunity to use some libraries by adding them in transformers construct.