Reapply support for X11 screenshare (#28160)

Reapplies #27807 after [revert due to not building on
ARM](https://github.com/zed-industries/zed/pull/28141) by updating scap
to include [a fix to its build on
ARM](08f0a01417)

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>

crates/gpui/src/platform.rs

@@ -26,6 +26,12 @@ mod test;
 #[cfg(target_os = "windows")]
 mod windows;
 
+#[cfg(all(
+    any(target_os = "linux", target_os = "freebsd"),
+    any(feature = "wayland", feature = "x11"),
+))]
+pub(crate) mod scap_screen_capture;
+
 use crate::{
     Action, AnyWindowHandle, App, AsyncWindowContext, BackgroundExecutor, Bounds,
     DEFAULT_WINDOW_SIZE, DevicePixels, DispatchEventResult, Font, FontId, FontMetrics, FontRun,
@@ -158,6 +164,7 @@ pub(crate) trait Platform: 'static {
         None
     }
 
+    fn is_screen_capture_supported(&self) -> bool;
     fn screen_capture_sources(
         &self,
     ) -> oneshot::Receiver<Result<Vec<Box<dyn ScreenCaptureSource>>>>;
@@ -246,13 +253,14 @@ pub trait PlatformDisplay: Send + Sync + Debug {
 /// A source of on-screen video content that can be captured.
 pub trait ScreenCaptureSource {
     /// Returns the video resolution of this source.
-    fn resolution(&self) -> Result<Size<Pixels>>;
+    fn resolution(&self) -> Result<Size<DevicePixels>>;
 
     /// Start capture video from this source, invoking the given callback
     /// with each frame.
     fn stream(
         &self,
-        frame_callback: Box<dyn Fn(ScreenCaptureFrame)>,
+        foreground_executor: &ForegroundExecutor,
+        frame_callback: Box<dyn Fn(ScreenCaptureFrame) + Send>,
     ) -> oneshot::Receiver<Result<Box<dyn ScreenCaptureStream>>>;
 }