[feature] static application blur

[Inderix]

I think it'd be neat to be able to set a static blur for apps like you can for dash-to-dock and the top panel blur, retaining the "look" of background blur in apps, but with better performance and the ability to use the rounded corner pipeline to fix the corner artifacts.

It'd also allow for replicating Microsoft's "Mica" material used in Fluent design apps and Windows 11:
https://learn.microsoft.com/en-us/windows/apps/design/style/mica