[sddm-theme] Style the session and keyboard layout selectors to be more Breeze
Summary:
The session selector's and keyboard layout's menus are now styled to resemble the Breeze theme rather than the default QML style.
BUG: 408702
Test Plan: Ensure the styling looks good regardless of various conditions. (resolution, dpi, distro, amount of sessions, etc.)
Reviewers: VDG, filipf
Reviewed By: VDG, filipf
Subscribers: apol, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D21794