Final shader should not be applied on overlay

[Meakk]

Describe the bug
Overlay widgets like filename or cheatsheet should be drawn after the final shader

[samoncrief]

I would like to work on this, though I'm still trying to dig up how the draw order and shaders are applied.

[mwestphal]

Awesome, I just assigned it to you.

[Meakk]

@samoncrief this one is challenging. Currently, there is a main pass taking care of everything (background, scene and overlay), then the userpass is postprocessing the result.
Basically, the overlay step in the main pass should be extracted to its own pass and be applied after the user pass.
Don't hesitate to ping me on Discord if you need to discuss

[mwestphal]

Done in #1984