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/app.rs

@@ -33,8 +33,8 @@ use crate::{
     Entity, EventEmitter, ForegroundExecutor, Global, KeyBinding, Keymap, Keystroke, LayoutId,
     Menu, MenuItem, OwnedMenu, PathPromptOptions, Pixels, Platform, PlatformDisplay, Point,
     PromptBuilder, PromptHandle, PromptLevel, Render, RenderablePromptHandle, Reservation,
-    SharedString, SubscriberSet, Subscription, SvgRenderer, Task, TextSystem, View, ViewContext,
-    Window, WindowAppearance, WindowContext, WindowHandle, WindowId,
+    ScreenCaptureSource, SharedString, SubscriberSet, Subscription, SvgRenderer, Task, TextSystem,
+    View, ViewContext, Window, WindowAppearance, WindowContext, WindowHandle, WindowId,
 };
 
 mod async_context;
@@ -599,6 +599,13 @@ impl AppContext {
         self.platform.primary_display()
     }
 
+    /// Returns a list of available screen capture sources.
+    pub fn screen_capture_sources(
+        &self,
+    ) -> oneshot::Receiver<Result<Vec<Box<dyn ScreenCaptureSource>>>> {
+        self.platform.screen_capture_sources()
+    }
+
     /// Returns the display with the given ID, if one exists.
     pub fn find_display(&self, id: DisplayId) -> Option<Rc<dyn PlatformDisplay>> {
         self.displays()