try to enforce borders settings from KWin

Summary:
this makes the "no borders" option do something: however it cause many
other issues with many themes that weren't really designed for "no
borders"
it fixes the "tiny borders" for almost all themes, as the whole calculation before
was
completely wrong

Test Plan:
Some themes work way better now, some look broken with no border or no side borders
some look perfect with those options
another issue is that aurorae is going to support no borders, it has to support like
breeze resizing from the shadows

Reviewers: #plasma, #kwin, davidedmundson

Reviewed By: #plasma, #kwin, davidedmundson

Subscribers: davidedmundson, ngraham, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D25146