Post-release hotfix for x11/plasma5-plasma-desktop

The "lock/unlock widgets" feature is now hidden in Plasma (it used to
be a big obvious thing, using up screen real-estate). They are now
unlocked by default, but if a user had locked them in 5.17, and
upgrades to 5.18, there's no way to unlock.

Upstream bug:
https://bugs.kde.org/show_bug.cgi?id=417424

We just import the same patch (an extra .js file to run during update

• this is handled by Plasma itself).