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
Cache result of processing and inline the check
Make sure supertypes are unique

`array_flip` followed by `array_keys` is much quicker than `array_unique`. We don't retain he array indices by doing this, but we don't need them in this case so can take advantage of the optimisation. Making the supertypes array unique reduces the amount of classes that DI has to work through.