Overlay decoration for windows that don't export the menubar

[developer91234]

Might be beyond scope, but allowing the decoration to cut into the window chrome would open up some interesting possibilities for apps that either lack a menubar or fail to export it, as well as for CSD windows that insist on their own idiosyncratic window decoration.

I'm thinking to overlay a draggable titlebar strip of variable length, customizable on an individual app basis. Something like the image below except the overlay strip span the width of the window and be transparent except for the window controls which would blend with the window chrome:

https://github.com/jinliu/kwin-deco-chromi