Nested arrays of entities need to get PUT semantics applied for merge patch

[odrotbohm]

In the course of debugging #2357, it occurred that the nested array handling applies patch semantics for entities. This seems to have been originally requested in #1294, but is essentially wrong. First tests reveal that except a test particularly implementing the expectation within the ticket, no other tests failed.

We should correct that for the upcoming milestone, but not port the change back as it might subtly break existing systems.