Preserve the fluent interface
#6398 - minor CS fixes (spacing, return type)
#6398 - minor CS fixes (spacing, return type)
#6398 - type fix (`listenersToDetach` may be `null`)
#6398 - test case to enforce fluent interface on `Forward#setListenersToDetach()`
#6398 - Adding missing test-case properties and type-hints
Merge branch 'hotfix/#6398-forward-controller-plugin-fluent-interface-consistency'

Close #6398