gpui: Make screen capture dependency optional (#32937)

Add `screen-capture` feature to gpui to enable screen capture support.  The motivation for this is to make dependencies on scap / x11 / xcb optional.

Release Notes:

- N/A

---------

Co-authored-by: Michael Sloan <michael@zed.dev>

crates/gpui/src/platform/linux/x11/client.rs

@@ -15,7 +15,6 @@ use calloop::{
     generic::{FdWrapper, Generic},
 };
 use collections::HashMap;
-use futures::channel::oneshot;
 use http_client::Url;
 use log::Level;
 use smallvec::SmallVec;
@@ -59,13 +58,12 @@ use crate::platform::{
         reveal_path_internal,
         xdg_desktop_portal::{Event as XDPEvent, XDPEventSource},
     },
-    scap_screen_capture::scap_screen_sources,
 };
 use crate::{
     AnyWindowHandle, Bounds, ClipboardItem, CursorStyle, DisplayId, FileDropEvent, Keystroke,
     LinuxKeyboardLayout, Modifiers, ModifiersChangedEvent, MouseButton, Pixels, Platform,
     PlatformDisplay, PlatformInput, PlatformKeyboardLayout, Point, RequestFrameOptions,
-    ScaledPixels, ScreenCaptureSource, ScrollDelta, Size, TouchPhase, WindowParams, X11Window,
+    ScaledPixels, ScrollDelta, Size, TouchPhase, WindowParams, X11Window,
     modifiers_from_xinput_info, point, px,
 };
 
@@ -1479,14 +1477,19 @@ impl LinuxClient for X11Client {
         ))
     }
 
+    #[cfg(feature = "screen-capture")]
     fn is_screen_capture_supported(&self) -> bool {
         true
     }
 
+    #[cfg(feature = "screen-capture")]
     fn screen_capture_sources(
         &self,
-    ) -> oneshot::Receiver<anyhow::Result<Vec<Box<dyn ScreenCaptureSource>>>> {
-        scap_screen_sources(&self.0.borrow().common.foreground_executor)
+    ) -> futures::channel::oneshot::Receiver<anyhow::Result<Vec<Box<dyn crate::ScreenCaptureSource>>>>
+    {
+        crate::platform::scap_screen_capture::scap_screen_sources(
+            &self.0.borrow().common.foreground_executor,
+        )
     }
 
     fn open_window(