TASK: cleanup node service

[mhsdesign]

i leveraged

$this->contentRepositoryRegistry->subgraphForNode($node)
            ->findClosestNode($node->nodeAggregateId, FindClosestNodeFilter::create(nodeTypeConstraints: NodeTypeNameFactory::NAME_DOCUMENT));

over manually iterating over the parents. Helper methods were inlined in the few places used.
The "NodeService" was renamed to something which seems more internal and should not be used from outside ;)

What I did

How I did it

How to verify it

requires neos/neos-development-collection#4601 to be merged first.

[nezaniel]

Fine by me