A backwards-compatibility layer has been added to persistence to help
consumers move to the new namespacing. It is based on class aliases,
which means the type declaration changes should not be a BC-break: types
are the same.
See doctrine/persistence#71

This means:
- using the new namespaces
- adding autoload calls for new types to types that may be extended and
use persistence types in methods signatures for which compatibility
checks may happen,
so that signature compatibility is recognized by old versions of php.
More details on this at
https://dev.to/greg0ire/how-to-deprecate-a-type-in-php-48cf

Fixes #616 as a side effect, but the real fix is at
symfony/symfony#35728

…stence

Address deprecations from persistence library