[v2 Linux] Transparent window on linux

[lyimmi]

Is your feature request related to a problem? Please describe.

Currently in v2 we can use a transparent window on Windows and Mac, but Linux is missing this feature.

I would like to be able to use transparent windows on Linux as well.

Describe the solution you'd like

I would like to add the transparent window functionality to internal/frontend/desktop/linux/window.go and a new option to linux.Options to enable it.

I was able achieve window transparency without any blur/frosting effect. (I think blur could be added in GTK4)

If it is ok to add before v2.1.0 (it is not in the road map) I'd be happy to make a PR for it.

Describe alternatives you've considered

Did not consider anything else.

Additional context

[leaanthony]

Awesome! Feel free to make a PR for this. Feature parity is important!