Move the inline installer progress cancel button to the left side
Summary: This prevents the progress view from jumping around, and keeps it right-aligned just like the button it replaces
Test Plan:
Reviewers: apol, Discover Software Store
Reviewed By: apol, Discover Software Store
Subscribers: andreaska, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D13006