This Merge Request adds support for the "Tools Area" proposed in https://phabricator.kde.org/T10201.
In essence, Breeze now draws a horizontal line below the menubar or toolbar for QWidgets-based apps, to
distinguish it from the content area below. Additionally, when using a color scheme with
the backgrounds of the toolbars, menubar, and titlebar are all drawn with the same color, resulting in a
unified appearance for the top of the window.
This is how it looks in conjunction with a color scheme using
(e.g. !2 (merged)):