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/test_context.rs

@@ -4,8 +4,8 @@ use crate::{
     Element, Empty, Entity, EventEmitter, ForegroundExecutor, Global, InputEvent, Keystroke, Model,
     ModelContext, Modifiers, ModifiersChangedEvent, MouseButton, MouseDownEvent, MouseMoveEvent,
     MouseUpEvent, Pixels, Platform, Point, Render, Result, Size, Task, TestDispatcher,
-    TestPlatform, TestWindow, TextSystem, View, ViewContext, VisualContext, WindowBounds,
-    WindowContext, WindowHandle, WindowOptions,
+    TestPlatform, TestScreenCaptureSource, TestWindow, TextSystem, View, ViewContext,
+    VisualContext, WindowBounds, WindowContext, WindowHandle, WindowOptions,
 };
 use anyhow::{anyhow, bail};
 use futures::{channel::oneshot, Stream, StreamExt};
@@ -287,6 +287,12 @@ impl TestAppContext {
         self.test_window(window_handle).simulate_resize(size);
     }
 
+    /// Causes the given sources to be returned if the application queries for screen
+    /// capture sources.
+    pub fn set_screen_capture_sources(&self, sources: Vec<TestScreenCaptureSource>) {
+        self.test_platform.set_screen_capture_sources(sources);
+    }
+
     /// Returns all windows open in the test.
     pub fn windows(&self) -> Vec<AnyWindowHandle> {
         self.app.borrow().windows().clone()