Corfu face simplifications
I just rewrote the display code of Corfu to use child frames exclusively, since I could not make the overlays sufficiently robust. This comes at the cost of the support for the text mode ui. As a result the face definitions got a bit simpler and you may want to revise the definitions used in Modus. Background, border and bar faces should only specify a :background face property. The other face properties are ignored.