Fix missing modifier changed events on Linux X11 (#24154)

Release Notes:

- Fixed some modifier changed events not being present on Linux X11.
This affected things like the project search palette, where holding ctrl
would not cause the split options to appear.

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

@@ -186,6 +186,8 @@ pub struct X11ClientState {
     pub(crate) ximc: Option<X11rbClient<Rc<XCBConnection>>>,
     pub(crate) xim_handler: Option<XimHandler>,
     pub modifiers: Modifiers,
+    // TODO: Can the other updates to `modifiers` be removed so that this is unnecessary?
+    pub last_modifiers_changed_event: Modifiers,
 
     pub(crate) compose_state: Option<xkbc::compose::State>,
     pub(crate) pre_edit_text: Option<String>,
@@ -434,6 +436,7 @@ impl X11Client {
 
         X11Client(Rc::new(RefCell::new(X11ClientState {
             modifiers: Modifiers::default(),
+            last_modifiers_changed_event: Modifiers::default(),
             event_loop: Some(event_loop),
             loop_handle: handle,
             common,
@@ -867,11 +870,12 @@ impl X11Client {
                 }
 
                 let modifiers = Modifiers::from_xkb(&state.xkb);
-                if state.modifiers == modifiers {
+                if state.last_modifiers_changed_event == modifiers {
                     drop(state);
                 } else {
                     let focused_window_id = state.keyboard_focused_window?;
                     state.modifiers = modifiers;
+                    state.last_modifiers_changed_event = modifiers;
                     drop(state);
 
                     let focused_window = self.get_window(focused_window_id)?;