Custom blur region for widget background

[luisbocanegra]

Similar to https://github.com/luisbocanegra/plasma-panel-colorizer/issues/50 but per widget.

Todo:

• [x] Pass the rectangles and spacing to c++ and create the blur region with proper spacing
• [x] Determine whether or not show widget blur regions if custom panel background is enabled

[luisbocanegra]

It works!

Depending on the radius/wallpaper/Plasma theme it will show a bit of korners bug but looks good enough at least with the default Breeze ContrastEffect values. The image above has the following values:

[ContrastEffect]
enabled=true
contrast=0.7
intensity=1
saturation=8