Make some private functions internal to allow the developpement of "withSignature" functions (like permit) (#2568)

* add internal _setOwner in Ownable

* address issues raised in #2567

* updte changelog entry

* improve changelog and documentation

* rephrasing doc

* add cahngelog improvement lost in merge

* notify deprecation of _setupRole in changelog

* Demote caution to note

* Update CHANGELOG.md

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>