[Updates page] use fancier logic for handling elided Old+New version strings
Summary:
@broulik taught me how to do this! It's more robust than the current logic, which
doesn't expand to the full form when the window becomes wide enough to show the
whole string without eliding.
Test Plan:
Reviewers: apol, broulik, Discover Software Store
Reviewed By: apol, Discover Software Store
Subscribers: mart, broulik, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D24713