[Folder view] Fix binding loop on width

Summary:
This fixes the binding loop and replaces a complicated bit of code with something much
simpler.

Test Plan:
No more binding loop warning when running plasmashell on the CLI

No meaningful difference in appearance for every combination of icon size and label
width in icon view

Reviewers: Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: davidedmundson, gvgeo, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D27261