Merge branch 'cs/#6921-remove-unused-variable-assignments'

Close #6921
allow to set DateTimeObject to the expires SetCookie expire ref #6673
added docblock comment
added missing docblock
fix BC for #6890 and c91bd9be56e0b194beedde4c78be943591cdc719
fix CS
fix CS
removed slash for datetime docs
#6924 #6890 - avoiding unused `is_a()` call
#6924 - minor CS fixes in test cases
#6924 - cs fixes: avoiding variables overwrites and removing useless IDE hints
Merge branch 'hotfix/#6924-#6890-abstract-platform-bc-break-revert' into develop

Close #6924
#6673 - importing used `DateTime` class
#6923 #6673 - minor docblock CS fixes
#6923 #6673 - adding missing `@group` annotations for newly introduced tests
Merge branch 'feature/#6923-allow-datetime-cookie-expires'

Close #6923
Merge branch 'feature/#6923-allow-datetime-cookie-expires' into develop

Close #6923
Forward port #6923
added zendframework/zend-cache into Zend\XmlRpc's composer.json
to support Zend\\XmlRpc\\Server\\Cache usage
Merge branch 'dependencies/#6932-zend-xmlrpc-may-require-zend-cache'

Close #6932
Merge branch 'dependencies/#6932-zend-xmlrpc-may-require-zend-cache' into develop

Close #6932
Forward port #6932