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/mac/platform.rs

@@ -1,14 +1,14 @@
 use super::{
     attributed_string::{NSAttributedString, NSMutableAttributedString},
     events::key_to_native,
-    BoolExt,
+    renderer, screen_capture, BoolExt,
 };
 use crate::{
     hash, Action, AnyWindowHandle, BackgroundExecutor, ClipboardEntry, ClipboardItem,
     ClipboardString, CursorStyle, ForegroundExecutor, Image, ImageFormat, Keymap, MacDispatcher,
     MacDisplay, MacWindow, Menu, MenuItem, PathPromptOptions, Platform, PlatformDisplay,
-    PlatformTextSystem, PlatformWindow, Result, SemanticVersion, Task, WindowAppearance,
-    WindowParams,
+    PlatformTextSystem, PlatformWindow, Result, ScreenCaptureSource, SemanticVersion, Task,
+    WindowAppearance, WindowParams,
 };
 use anyhow::anyhow;
 use block::ConcreteBlock;
@@ -58,8 +58,6 @@ use std::{
 };
 use strum::IntoEnumIterator;
 
-use super::renderer;
-
 #[allow(non_upper_case_globals)]
 const NSUTF8StringEncoding: NSUInteger = 4;
 
@@ -552,6 +550,12 @@ impl Platform for MacPlatform {
             .collect()
     }
 
+    fn screen_capture_sources(
+        &self,
+    ) -> oneshot::Receiver<Result<Vec<Box<dyn ScreenCaptureSource>>>> {
+        screen_capture::get_sources()
+    }
+
     fn active_window(&self) -> Option<AnyWindowHandle> {
         MacWindow::active_window()
     }