Allow Shift + Scroll to Horizontally Scroll in X11 and Wayland (#13676)

Release Notes:

- Allows shift + scroll horizontal scrolling on X11 and Wayland.

[Screencast from 2024-06-29
17-17-59.webm](https://github.com/zed-industries/zed/assets/14155062/2cac77b9-ecc8-4ddb-b08d-b5d964c8dc84)

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

@@ -817,10 +817,15 @@ impl X11Client {
 
                             if let Some(old_scroll) = old_scroll {
                                 let delta_scroll = old_scroll - new_scroll;
+                                let (x, y) = if !modifiers.shift {
+                                    (0.0, delta_scroll)
+                                } else {
+                                    (delta_scroll, 0.0)
+                                };
                                 window.handle_input(PlatformInput::ScrollWheel(
                                     crate::ScrollWheelEvent {
                                         position,
-                                        delta: ScrollDelta::Lines(Point::new(0.0, delta_scroll)),
+                                        delta: ScrollDelta::Lines(Point::new(x, y)),
                                         modifiers,
                                         touch_phase: TouchPhase::default(),
                                     },