Merge branch 'version/bump'

Bump to 2.3.4dev
PHPCS fixes for Zend\Valiator
Merge branch 'cs/#6540-zend-validator-cs-fixes' into develop

Close #6540
PHPCS fixes for Zend\Escaper
Merge branch 'cs/#6538-zend-escaper-cs-fixes' into develop

Close #6538
PHPCS fixes for Zend\XmlRpc
Merge branch 'cs/#6682-zend-xmlrpc-cs-fixes' into develop

Close #6682
PHPCS fixes for Zend\Uri
Merge branch 'cs/#6683-zend-uri-cs-fixes' into develop

Close #6683
change is_null to $value compare to null
for consistency with #3520
Merge branch 'hotfix/#6643-is-null-removal' into develop

Forward port #6643
Merge branch 'develop' of https://github.com/zendframework/zf2 into feature/newlines-code-scanner