windows: Fix cursor style not changing when hovering over items in the title bar (#22580)

Closes #22578

Currently, the `hovered` boolean in the window state is only updated by
the `WM_MOUSELEAVE` event, which fires when the mouse cursor leaves the
window's working area. This means that when the user moves the cursor
from the window to the title bar, `hovered` is set to `false`. Later in
the code, this flag is used to determine the cursor style and check if
the cursor is over the correct window.

The `hovered` boolean should remain active even when the mouse is over
non-client items, such as the title bar or window borders. This PR fixes
that by using `WM_NCMOUSELEAVE` event, which is triggered when the mouse
leaves non-client items. This event is used to update the `hovered`
boolean accordingly.

Now, `hovered` is `true` when the mouse is over the window's working
area, as well as non-client areas like the title bar.

More context:

- Existing: `dwFlags: TME_LEAVE` tracks window area mouse leaves, which
is used in `handle_mouse_move_msg` func.
- New: `dwFlags: TME_LEAVE | TME_NONCLIENT` tracks non-client mouse
leaves, which is used in `handle_nc_mouse_move_msg` func.

Preview:


https://github.com/user-attachments/assets/b319303f-81b9-45cb-bf0c-535a59b96561

Release Notes:

- Fix cursor style not changing on hover over items in the title bar on
Windows

crates/gpui/src/platform/windows/events.rs

@@ -47,6 +47,7 @@ pub(crate) fn handle_msg(
         WM_MOUSEMOVE => handle_mouse_move_msg(handle, lparam, wparam, state_ptr),
         WM_MOUSELEAVE => handle_mouse_leave_msg(state_ptr),
         WM_NCMOUSEMOVE => handle_nc_mouse_move_msg(handle, lparam, state_ptr),
+        WM_NCMOUSELEAVE => handle_nc_mouse_leave_msg(state_ptr),
         WM_NCLBUTTONDOWN => {
             handle_nc_mouse_down_msg(handle, MouseButton::Left, wparam, lparam, state_ptr)
         }
@@ -314,6 +315,18 @@ fn handle_mouse_move_msg(
     Some(1)
 }
 
+fn handle_nc_mouse_leave_msg(state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
+    let mut lock = state_ptr.state.borrow_mut();
+    lock.hovered = false;
+    if let Some(mut callback) = lock.callbacks.hovered_status_change.take() {
+        drop(lock);
+        callback(false);
+        state_ptr.state.borrow_mut().callbacks.hovered_status_change = Some(callback);
+    }
+
+    Some(0)
+}
+
 fn handle_mouse_leave_msg(state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
     let mut lock = state_ptr.state.borrow_mut();
     lock.hovered = false;
@@ -971,6 +984,27 @@ fn handle_nc_mouse_move_msg(
         return None;
     }
 
+    let mut lock = state_ptr.state.borrow_mut();
+    if !lock.hovered {
+        lock.hovered = true;
+        unsafe {
+            TrackMouseEvent(&mut TRACKMOUSEEVENT {
+                cbSize: std::mem::size_of::<TRACKMOUSEEVENT>() as u32,
+                dwFlags: TME_LEAVE | TME_NONCLIENT,
+                hwndTrack: handle,
+                dwHoverTime: HOVER_DEFAULT,
+            })
+            .log_err()
+        };
+        if let Some(mut callback) = lock.callbacks.hovered_status_change.take() {
+            drop(lock);
+            callback(true);
+            state_ptr.state.borrow_mut().callbacks.hovered_status_change = Some(callback);
+        }
+    } else {
+        drop(lock);
+    }
+
     let mut lock = state_ptr.state.borrow_mut();
     if let Some(mut callback) = lock.callbacks.input.take() {
         let scale_factor = lock.scale_factor;