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/linux/platform.rs

@@ -35,8 +35,8 @@ use crate::{
     px, Action, AnyWindowHandle, BackgroundExecutor, ClipboardItem, CursorStyle, DisplayId,
     ForegroundExecutor, Keymap, Keystroke, LinuxDispatcher, Menu, MenuItem, Modifiers, OwnedMenu,
     PathPromptOptions, Pixels, Platform, PlatformDisplay, PlatformInputHandler, PlatformTextSystem,
-    PlatformWindow, Point, PromptLevel, Result, SemanticVersion, SharedString, Size, Task,
-    WindowAppearance, WindowOptions, WindowParams,
+    PlatformWindow, Point, PromptLevel, Result, ScreenCaptureSource, SemanticVersion, SharedString,
+    Size, Task, WindowAppearance, WindowOptions, WindowParams,
 };
 
 pub(crate) const SCROLL_LINES: f32 = 3.0;
@@ -242,6 +242,14 @@ impl<P: LinuxClient + 'static> Platform for P {
         self.displays()
     }
 
+    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> {
         self.active_window()
     }