Add support for laminas-hydrator ^4.0

This PR adds support for laminas-hydrator:^4.0. Laminas hydrator 4.0.0 comes with one BC break:

laminas/laminas-hydrator#30: Allow anonymous object usage with hydrators thanks to @weierophinney and @luiz-brandao-jr

This can be easily covered by adding the optional parameter ?object $instance = null to Doctrine\Laminas\Hydrator\Filter\PropertyName::filter(). Adding this parameter is still backward compatible to laminas-hydrator:^3.0, hence, both 3.0 and 4.0 series are now allowed in composer.json.

This PR will:

for php=7.2 use laminas-hydrator=^3.0 and laminas-stdlib=3.2.*
for php=^7.3 use laminas-hydrator=^4.0 and laminas-stdlib=^3.3

I suggest releasing this as a minor release, i.e. 2.1.0.

doctrine / doctrine-laminas-hydrator

Add support for laminas-hydrator ^4.0 #17