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/mac/platform.rs

@@ -552,6 +552,10 @@ impl Platform for MacPlatform {
             .collect()
     }
 
+    fn is_screen_capture_supported(&self) -> bool {
+        true
+    }
+
     fn screen_capture_sources(
         &self,
     ) -> oneshot::Receiver<Result<Vec<Box<dyn ScreenCaptureSource>>>> {