Investigate issues with semi-transparent drawing on transparent windows

[ecton]

From Discord @danbulant reports that on Wayland when transparent buttons shift between completely transparent and solid, the window becomes transparent rather than the solid color behind the widget remaining present. Here's a video demonstrating how when hovering the buttons the window temporarily becomes transparent:

UeUWECk.mp4

I verified that basic blending of stacked shapes is working correctly in Kludgine but I don't currently have an easy way to test transparent windows.

I'm wondering if there's something incorrect about how the alpha channel is being handled in transparent windows specifically, but another test to try is to render a semi-transparent button over a container to a texture to see if this can be reproduced purely in wgpu or whether it only affects transparent windows.