extract parent path in controllers

[martinlippert]

In case a controller does not have a common parent path defined on the class level using a @RequestMapping annotation, but all the embodied request mappings inside the class share the same prefix, we should offer a validation and a code action for this to extract the common parent path into a @RequestMapping annotation at the class level.

[martinlippert]

On top of this, it might be useful to implement this as an auto completion as well, so that when users type @RequestMapping at the class level, the commonly used parent path is suggested and if applied, automatically removed from the other request mapping annotations.