Add media extension for formatter

[jordisala1991]

Subject

I am targeting this branch, because this is in preparation for 5.0.

Changelog

### Added
- Added `MediaExtension` to render Media inside Formatters.
- Added ability to use Twig runtimes on your Formatter Extensions via `getAllowedRuntimes`.

[jordisala1991]

WDYT @VincentLanglet ? I had to add some stuff to make it work with Runtimes because otherwise don't get loaded by those custom Twig Environments.

[jordisala1991]

There are 2 things in this PR:

1. Trying to solve the MediaExtension issue: It is implemented on MediaBundle but completely broken. It should be implemented here.

2. With Runtimes of twig we can separate extensions and their logics. The problem is that we cant use them on formatters if we dont configure the Environment. Currently without this Pr there is no way someone can add a custom extension for formatters is those use Runtimes (like the media extension does).

If we agree on implementation I can add missing docs and polish it a little bit.

[VincentLanglet]

If we agree on implementation I can add missing docs and polish it a little bit.

Except our little discussion, I'm fully ok with it.

[VincentLanglet]

Is it ready to merge ?

[VincentLanglet]

If I understand correctly, we should provide a PR to deprecate https://github.com/sonata-project/SonataMediaBundle/blob/4.x/src/Twig/Extension/FormatterMediaExtension.php isn't it ?

[jordisala1991]

I would say we should remove it directly. That class does nothing and it is not registered on the container.

[VincentLanglet]

I would say we should remove it directly. That class does nothing and it is not registered on the container.

Removing something is theoretically a BC-break, but this seems ok to me.