Write the visit in Kernel TERMINATE event

This was more work than expected. Since the patch fails to apply I coded it by hand. The thing is this patch worked only for entity types of Node, while the module is supposed to support any entity type, also implemented it using dependency injection. Fixed the tests and added doc comments.

There is also a similar fix in 📌 Disabled page caching Needs review but using a different event. That one adds content to a recently read table on KernelEvent::REQUEST, so they are added before the page is loaded to the client, I go a bit into details in comment #11.

Okay, so it looks like this will not work for anonymous users, at least not after the first session is created in recently_read_entity_view(). This happens because hook_entity_view() runs only when the view is not cached. So this will have to be moved somewhere else.

I moved the anonymous session check to an event subscriber, that runs on KernelEvents::REQUEST on priority 27. This way the session check for anonymous users gets done even if the page is already cached.