Panel: rounded corners draw artifacts to the edges of the screen

[leviport]

I've confirmed this on mega-r3 with a 4090, and my bonw14 with a 2080, so this might be NVIDIA-related. On both, this was appearing on a fresh COSMIC DE installation on 22.04 without any further customization. popdev:master was added on both, and all updates were installed.

The default dock with round corners shows an artifact from the corners to the edges of the screen:

Setting a panel gap spawns artifacts on the bottom rounded corners as well:

And changing the corner roundness changes the sizes of the artifacts:

[wash2]

#189 & #194 are probably related. I'm going to try to switch how the panel background is rendered in the overflow branch now that it can use iced elements, so that may fix this issue.

[XV-02]

As a note, I am also seeing these artifacts on VM created with virtual machine manager.

[wash2]

This issue is probably fixed now that the overflow branch is merged.