The current implementation of the exporters are not taking the entity
listeners into account. I have added test cases for most of the edge
cases I could think of and implemented the Exporter handling.
This PR originates from https://github.com/doctrine/doctrine2/pull/5864,
I was overwhelmed by the amount of conflicts I had to resolve so I
started anew on a clean master HEAD.
Squashed commits:
- Code review aftermath
- Add even more return type declarations
- Added `return null` to methods declared with nullable return types
- Removed unneeded docblocks when types are self-explanatory
