Use LiveKit's Rust SDK on Linux while continue using Swift SDK on Mac (#21550)

Similar to #20826 but keeps the Swift implementation. There were quite a
few changes in the `call` crate, and so that code now has two variants.

Closes #13714

Release Notes:

- Added preliminary Linux support for voice chat and viewing
screenshares.

---------

Co-authored-by: Kirill Bulatov <mail4score@gmail.com>
Co-authored-by: Kirill Bulatov <kirill@zed.dev>
Co-authored-by: Mikayla <mikayla@zed.dev>

crates/gpui/src/platform/windows/platform.rs

@@ -325,6 +325,14 @@ impl Platform for WindowsPlatform {
         WindowsDisplay::primary_monitor().map(|display| Rc::new(display) as Rc<dyn PlatformDisplay>)
     }
 
+    fn screen_capture_sources(
+        &self,
+    ) -> oneshot::Receiver<Result<Vec<Box<dyn ScreenCaptureSource>>>> {
+        let (mut tx, rx) = oneshot::channel();
+        tx.send(Err(anyhow!("screen capture not implemented"))).ok();
+        rx
+    }
+
     fn active_window(&self) -> Option<AnyWindowHandle> {
         let active_window_hwnd = unsafe { GetActiveWindow() };
         self.try_get_windows_inner_from_hwnd(active_window_hwnd)