Allow to decorate dependency factory services

[goetas]

Q	A
Type	feature
BC Break	-
Fixed issues	-

Summary

The DI factory become a central extension point for doctrine migrations.
Being able to decorate services is fundamental for most of DI containers and allows to apply composition over inheritance

[goetas]

thinking it twice, this is already possible by doing

$oldComparator = $di->getComparator();
$oldComparator->setComparator(new NewComparator($oldComparator));