Add types to entity manager

[derrabus]

This PR adds native parameter, return and property types to our entity manager implementations.

[derrabus]

As soon as we add return types, this test is broken beyond repair because it violates the type contracts almost everywhere. 🙁

[derrabus]

Waiting for #9293

[SenseException]

How did you decide where you wanted to add a type and where not?

For example, why did $className get no type?

    public function getClassMetadata($className): ClassMetadata
    {
        return parent::getClassMetadata($className);
    }

[derrabus]

How did you decide where you wanted to add a type and where not?

I want to add them everywhere. 🙂

For example, why did $className get no type?

    public function getClassMetadata($className): ClassMetadata
    {
        return parent::getClassMetadata($className);
    }

The interface that is implemented here originates in the persitence repository:

https://github.com/doctrine/persistence/blob/9f226731048d8efbd42e3b0079c6fc353f3a6b96/lib/Doctrine/Persistence/ObjectManager.php#L124-L138

PHP does not allow me to add native parameter types downstream (except for mixed that is). So the type would need to be added to the ObjectManager interface first before we can proceed here. I could declare the parameter as mixed, but I'd rather leave it untyped until the persistence has been patched with types in a stable release. Does that make sense?

[SenseException]

Yep, I forgot about the dependency to Persistence and a reminder to update it too.