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](https://github.com/zed-industries/scap/commit/08f0a01417505cc0990b9931a37e5120db92e0d0)

Release Notes:

- N/A

---------

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

crates/gpui/src/platform/test/platform.rs

@@ -1,7 +1,8 @@
 use crate::{
-    AnyWindowHandle, BackgroundExecutor, ClipboardItem, CursorStyle, ForegroundExecutor, Keymap,
-    Platform, PlatformDisplay, PlatformTextSystem, ScreenCaptureFrame, ScreenCaptureSource,
-    ScreenCaptureStream, Task, TestDisplay, TestWindow, WindowAppearance, WindowParams, px, size,
+    AnyWindowHandle, BackgroundExecutor, ClipboardItem, CursorStyle, DevicePixels,
+    ForegroundExecutor, Keymap, Platform, PlatformDisplay, PlatformTextSystem, ScreenCaptureFrame,
+    ScreenCaptureSource, ScreenCaptureStream, Size, Task, TestDisplay, TestWindow,
+    WindowAppearance, WindowParams, size,
 };
 use anyhow::Result;
 use collections::VecDeque;
@@ -46,13 +47,14 @@ 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 resolution(&self) -> Result<Size<DevicePixels>> {
+        Ok(size(DevicePixels(1), DevicePixels(1)))
     }
 
     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>>> {
         let (mut tx, rx) = oneshot::channel();
         let stream = TestScreenCaptureStream {};
@@ -271,6 +273,10 @@ impl Platform for TestPlatform {
         Some(self.active_display.clone())
     }
 
+    fn is_screen_capture_supported(&self) -> bool {
+        true
+    }
+
     fn screen_capture_sources(
         &self,
     ) -> oneshot::Receiver<Result<Vec<Box<dyn ScreenCaptureSource>>>> {