linux/x11: Restore differentiation of mouse/keyboard focus (#13995)

This restores https://github.com/zed-industries/zed/pull/13943 which was
reverted in #13974 because it was possible to get in a state where focus
could not be restored on a window.

In this PR there's an additional change: `FocusIn` and `FocusOut` events
are always handled, even if the `event.mode` is not "NORMAL". In my
testing, `alt-tabbing` between windows didn't produce `FocusIn` and
`FocusOut` events when we had that check. Now, with the check removed,
it's possible to switch focus between two windows again with `alt-tab`.


Release Notes:

- N/A

---------

Co-authored-by: Conrad <conrad@zed.dev>
Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/gpui/src/window.rs

@@ -541,6 +541,7 @@ pub struct Window {
     appearance: WindowAppearance,
     appearance_observers: SubscriberSet<(), AnyObserver>,
     active: Rc<Cell<bool>>,
+    hovered: Rc<Cell<bool>>,
     pub(crate) dirty: Rc<Cell<bool>>,
     pub(crate) needs_present: Rc<Cell<bool>>,
     pub(crate) last_input_timestamp: Rc<Cell<Instant>>,
@@ -672,6 +673,7 @@ impl Window {
         let text_system = Arc::new(WindowTextSystem::new(cx.text_system().clone()));
         let dirty = Rc::new(Cell::new(true));
         let active = Rc::new(Cell::new(platform_window.is_active()));
+        let hovered = Rc::new(Cell::new(platform_window.is_hovered()));
         let needs_present = Rc::new(Cell::new(false));
         let next_frame_callbacks: Rc<RefCell<Vec<FrameCallback>>> = Default::default();
         let last_input_timestamp = Rc::new(Cell::new(Instant::now()));
@@ -778,7 +780,17 @@ impl Window {
                     .log_err();
             }
         }));
-
+        platform_window.on_hover_status_change(Box::new({
+            let mut cx = cx.to_async();
+            move |active| {
+                handle
+                    .update(&mut cx, |_, cx| {
+                        cx.window.hovered.set(active);
+                        cx.refresh();
+                    })
+                    .log_err();
+            }
+        }));
         platform_window.on_input({
             let mut cx = cx.to_async();
             Box::new(move |event| {
@@ -829,6 +841,7 @@ impl Window {
             appearance,
             appearance_observers: SubscriberSet::new(),
             active,
+            hovered,
             dirty,
             needs_present,
             last_input_timestamp,
@@ -1222,6 +1235,17 @@ impl<'a> WindowContext<'a> {
         self.window.active.get()
     }
 
+    /// Returns whether this window is considered to be the window
+    /// that currently owns the mouse cursor.
+    /// On mac, this is equivalent to `is_window_active`.
+    pub fn is_window_hovered(&self) -> bool {
+        if cfg!(target_os = "linux") {
+            self.window.hovered.get()
+        } else {
+            self.is_window_active()
+        }
+    }
+
     /// Toggle zoom on the window.
     pub fn zoom_window(&self) {
         self.window.platform_window.zoom();
@@ -2980,7 +3004,7 @@ impl<'a> WindowContext<'a> {
 
     fn reset_cursor_style(&self) {
         // Set the cursor only if we're the active window.
-        if self.is_window_active() {
+        if self.is_window_hovered() {
             let style = self
                 .window
                 .rendered_frame