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/test/platform.rs

@@ -1,7 +1,7 @@
 use crate::{
-    AnyWindowHandle, BackgroundExecutor, ClipboardItem, CursorStyle, ForegroundExecutor, Keymap,
-    Platform, PlatformDisplay, PlatformTextSystem, Task, TestDisplay, TestWindow, WindowAppearance,
-    WindowParams,
+    px, size, AnyWindowHandle, BackgroundExecutor, ClipboardItem, CursorStyle, ForegroundExecutor,
+    Keymap, Platform, PlatformDisplay, PlatformTextSystem, ScreenCaptureFrame, ScreenCaptureSource,
+    ScreenCaptureStream, Task, TestDisplay, TestWindow, WindowAppearance, WindowParams,
 };
 use anyhow::Result;
 use collections::VecDeque;
@@ -31,6 +31,7 @@ pub(crate) struct TestPlatform {
     #[cfg(any(target_os = "linux", target_os = "freebsd"))]
     current_primary_item: Mutex<Option<ClipboardItem>>,
     pub(crate) prompts: RefCell<TestPrompts>,
+    screen_capture_sources: RefCell<Vec<TestScreenCaptureSource>>,
     pub opened_url: RefCell<Option<String>>,
     pub text_system: Arc<dyn PlatformTextSystem>,
     #[cfg(target_os = "windows")]
@@ -38,6 +39,31 @@ pub(crate) struct TestPlatform {
     weak: Weak<Self>,
 }
 
+#[derive(Clone)]
+/// A fake screen capture source, used for testing.
+pub struct TestScreenCaptureSource {}
+
+pub struct TestScreenCaptureStream {}
+
+impl ScreenCaptureSource for TestScreenCaptureSource {
+    fn resolution(&self) -> Result<crate::Size<crate::Pixels>> {
+        Ok(size(px(1.), px(1.)))
+    }
+
+    fn stream(
+        &self,
+        _frame_callback: Box<dyn Fn(ScreenCaptureFrame)>,
+    ) -> oneshot::Receiver<Result<Box<dyn ScreenCaptureStream>>> {
+        let (mut tx, rx) = oneshot::channel();
+        let stream = TestScreenCaptureStream {};
+        tx.send(Ok(Box::new(stream) as Box<dyn ScreenCaptureStream>))
+            .ok();
+        rx
+    }
+}
+
+impl ScreenCaptureStream for TestScreenCaptureStream {}
+
 #[derive(Default)]
 pub(crate) struct TestPrompts {
     multiple_choice: VecDeque<oneshot::Sender<usize>>,
@@ -72,6 +98,7 @@ impl TestPlatform {
             background_executor: executor,
             foreground_executor,
             prompts: Default::default(),
+            screen_capture_sources: Default::default(),
             active_cursor: Default::default(),
             active_display: Rc::new(TestDisplay::new()),
             active_window: Default::default(),
@@ -114,6 +141,10 @@ impl TestPlatform {
         !self.prompts.borrow().multiple_choice.is_empty()
     }
 
+    pub(crate) fn set_screen_capture_sources(&self, sources: Vec<TestScreenCaptureSource>) {
+        *self.screen_capture_sources.borrow_mut() = sources;
+    }
+
     pub(crate) fn prompt(&self, msg: &str, detail: Option<&str>) -> oneshot::Receiver<usize> {
         let (tx, rx) = oneshot::channel();
         self.background_executor()
@@ -202,6 +233,20 @@ impl Platform for TestPlatform {
         Some(self.active_display.clone())
     }
 
+    fn screen_capture_sources(
+        &self,
+    ) -> oneshot::Receiver<Result<Vec<Box<dyn ScreenCaptureSource>>>> {
+        let (mut tx, rx) = oneshot::channel();
+        tx.send(Ok(self
+            .screen_capture_sources
+            .borrow()
+            .iter()
+            .map(|source| Box::new(source.clone()) as Box<dyn ScreenCaptureSource>)
+            .collect()))
+            .ok();
+        rx
+    }
+
     fn active_window(&self) -> Option<crate::AnyWindowHandle> {
         self.active_window
             .borrow()
@@ -330,6 +375,13 @@ impl Platform for TestPlatform {
     }
 }
 
+impl TestScreenCaptureSource {
+    /// Create a fake screen capture source, for testing.
+    pub fn new() -> Self {
+        Self {}
+    }
+}
+
 #[cfg(target_os = "windows")]
 impl Drop for TestPlatform {
     fn drop(&mut self) {