Add a new set of barcode size functions

Summary:
preferredSize() is an improvement over what minimumSize() used to do,
with taking the device pixel ratio into account. Additionally it also
works correctly for 1D codes now (ie. those are now scannable on a
standard DPI screen).

trueMinimumSize() is what minimumSize() should have been, ie. the absolute
minimum amount of pixels needed to display the code. This is mainly useful
for applications doing their own layouting/scaling logic, beyond what
preferredSize() offers.

minimumSize() becomes deprecated by this, the deprecation macros will
follow once the current users have been adjusted.

Reviewers: svuorela

Reviewed By: svuorela

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D27989