[WIP] refactor findMany()

Lets start with this one here...

The main purpose is to avoid many queries for `DocumentManager::findMany()`. The first step would be done with https://github.com/jackalope/jackalope-doctrine-dbal/pull/210 (when this occurs in other implementations, it should be solved too).
Here i solve the problem with many queries by creating the translation for every document. This problem occurs in `ChildTranslationStrategy` only, as they need to get a kind of a child node. Cause of that i created a `TranslationsNodesWarmer` (open for better names), which provide a method to pre-fetch all translations of a list of nodes.

Btw: i created a `getOrCreateDocument()` method in the UoW to handle that easier.

I did not look at any tests, just wanna show the idea.
here is the last problem i have got atm: as i touch a `NodePathIterator` i got batched queries, what would be fine. But after the first 50 nodes, this one stops to work and doesn't work on the following. These one are lost in the list of prepared (cached in the `ObjectManager`) and are queried one by one later when calling `UnitOfWork::doLoadTranslation()`.
Any idea how to query directly with the advantage of the `ObjectManager`? tried `getNodesByIdentifier()`, but this one is for identifieres (uuid) only. I would miss a `Session::getNodesByPath()`, which goes directly to the transport level. The current implementation of the session mixes `getNodes()` and `getNodesByPath()`.