KFormat: Use KFormat::JEDECBinaryDialect as default

That is using "Kb" instead of "Kib" by default for file sizes.

This was chosen as default in 3.5, but some code wasn't changed, or this was set some place else.

We can see it in https://invent.kde.org/frameworks/kdelibs4support/-/blob/kf5/src/kdecore/klocale.h?ref_type=heads#L526

Unless the default was changed back sometimes on purpose after KDE 3.5 ?

I think this is more aligned to what our users are accustomed to.

Related: https://bugs.kde.org/show_bug.cgi?id=453854 https://discuss.kde.org/t/how-to-configure-plasma-5-to-use-mb-instead-of-mib/5660/2

cc @ngraham

kio will need a similar patch.