Make KCheckAccelerators less invasive for apps that don't directly link to KXmlGui

Summary: BUGS: 337491

Test Plan:
Ran qtcreator and it no longer has the & in Details
Added some debug and checked that okular still gets the code called

Reviewers: anthonyfieroni

Reviewed By: anthonyfieroni

Subscribers: davidedmundson, anthonyfieroni, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D18204