Linux: Rewrite the event loop using calloop (#8314)

This PR unifies the event loop code for Wayland and X11. On Wayland,
blocking dispatch is now used. On X11, the invisible window is no longer
needed.

Release Notes:

- N/A

---------

Co-authored-by: Dzmitry Malyshau <kvark@fastmail.com>
Co-authored-by: Tadeo Kondrak <me@tadeo.ca>
Co-authored-by: Mikayla Maki <mikayla@zed.dev>
Co-authored-by: julia <julia@zed.dev>

crates/gpui/src/platform/linux/client.rs

@@ -4,7 +4,6 @@ use crate::platform::PlatformWindow;
 use crate::{AnyWindowHandle, DisplayId, PlatformDisplay, WindowOptions};
 
 pub trait Client {
-    fn run(&self, on_finish_launching: Box<dyn FnOnce()>);
     fn displays(&self) -> Vec<Rc<dyn PlatformDisplay>>;
     fn display(&self, id: DisplayId) -> Option<Rc<dyn PlatformDisplay>>;
     fn open_window(