As a side effect, this makes the code a bit more forward-compatible with
recent versions of PHPUnit, that have that return type declaration on
setUp().

Add void return type declaration to tests

That means:

- methods in final classes
- final methods (none of those found)
- private methods
- methods in Tests (that excludes setUp(), tearDown() and test*, which
  are handled with an automated tool in a separate commit)

Add type declarations where backwards compatible

In some scenarios involving long running processes and proxies,
resetting the entity manager results in a creation of a new entity
manager, while some services still hold a reference to the old one,
which keeps its previous state.

This abandons resetting the entity manager in favor of a call to clear()
on the existing entity manager if it is open.

Fixes #1112

…kernel-reset

Fix desynchronized entity managers after kernel reset

* 1.12.x:
  Clear open entity managers on kernel reset