collab: Add screen selector (#31506)

Instead of selecting a screen to share arbitrarily, we'll now allow user
to select the screen to share. Note that sharing multiple screens at the
time is still not supported (though prolly not too far-fetched).

Related to #4666

![image](https://github.com/user-attachments/assets/1afb664f-3cdb-4e0a-bb29-9d7093d87fa5)

Release Notes:

- Added screen selector dropdown to screen share button

---------

Co-authored-by: Kirill Bulatov <kirill@zed.dev>
Co-authored-by: Cole Miller <cole@zed.dev>

crates/livekit_client/src/livekit_client/playback.rs

@@ -326,11 +326,11 @@ pub(crate) async fn capture_local_video_track(
     capture_source: &dyn ScreenCaptureSource,
     cx: &mut gpui::AsyncApp,
 ) -> Result<(crate::LocalVideoTrack, Box<dyn ScreenCaptureStream>)> {
-    let resolution = capture_source.resolution()?;
+    let metadata = capture_source.metadata()?;
     let track_source = gpui_tokio::Tokio::spawn(cx, async move {
         NativeVideoSource::new(VideoResolution {
-            width: resolution.width.0 as u32,
-            height: resolution.height.0 as u32,
+            width: metadata.resolution.width.0 as u32,
+            height: metadata.resolution.height.0 as u32,
         })
     })?
     .await?;

crates/livekit_client/src/mock_client/participant.rs

@@ -5,7 +5,7 @@ use crate::{
 };
 use anyhow::Result;
 use collections::HashMap;
-use gpui::{AsyncApp, ScreenCaptureSource, ScreenCaptureStream};
+use gpui::{AsyncApp, ScreenCaptureSource, ScreenCaptureStream, TestScreenCaptureStream};
 
 #[derive(Clone, Debug)]
 pub struct LocalParticipant {
@@ -119,7 +119,3 @@ impl RemoteParticipant {
         self.identity.clone()
     }
 }
-
-struct TestScreenCaptureStream;
-
-impl gpui::ScreenCaptureStream for TestScreenCaptureStream {}