fix config dialogs in ltr mode
Summary:
anchor the layouts of config dialogs to left
this way they will look the same normally (they
are positioned at x 0 normally) but will be
anchored to right instead if layout mirroring is enabled
BUG:372721
Test Plan: opened all config dialogs both in ltr and ltr layouts
Reviewers: Plasma, davidedmundson
Reviewed By: Plasma, davidedmundson
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D3457