Add missing implementation for PolkitQt1::version*() API
Searching for the origin I used the unique sounding string "You can keep the string forever" and found some hits across KDE repos, Seems this was some unlucky copy & paste of https://invent.kde.org/unmaintained/kdelibs/-/blob/KDE/4.14/kdecore/util/kdeversion.h.cmake which though lost the cpp counterpart somewhere in one of the copies, as can be seen by e.g. attica or libtmdbqt also missing out that part :)
Let#s give it back here then at least, even if no-one seems to have missed it. Perhaps we could also just dump it because no one missed it?