compositor: Smoothen circle border

[MagneFire]

Smoothen borders such that the display blends into the bezel.

This PR is mostly meant as a means to start a discussion on if we want this functionality in the first place 😄

If we want this we probably also need to think about non-circular displays. Perhaps we can also enable this based on a device property. For instance this feature might make sense on sawfish (because of the huge bezel) but not on smelt which doesn't have a bezel (flat tire).

[FlorentRevest]

I originally introduced this for my bass where the screen borders seemed heavily pixelized, this was a cheap trick to make the screen look a bit better than it was :p (this was not about the thickness of the bezels) I still think it adds a nice polish to the AsteroidOS UI but maybe Timo has opinions on this ? At the time, I did not worry about flat tires but it could make sense to add a similar smoothing effect at the level of the flat tire maybe ?

Although it could make sense to compare a few smoothing options, I'd be leaning towards keeping this thing :)