gpui: Keep drag cursor style when dragging (#24797)

Release Notes:

- Improve to keep drag cursor style on dragging resize handles.

---

### Before


https://github.com/user-attachments/assets/d4100d01-ac02-42b8-b923-9f2b4633c458

### After


https://github.com/user-attachments/assets/b5a450cd-c6de-4b39-a79c-2d73fcbad209

With example:

```
cargo run -p gpui --example drag_drop
```


https://github.com/user-attachments/assets/4cba1966-1578-40ce-a435-64ec11bcace5

crates/gpui/src/elements/div.rs

@@ -1615,7 +1615,11 @@ impl Interactivity {
                                             global_id, hitbox, &style, window, cx,
                                         );
 
-                                        if !cx.has_active_drag() {
+                                        if let Some(drag) = cx.active_drag.as_ref() {
+                                            if let Some(mouse_cursor) = drag.cursor_style {
+                                                window.set_cursor_style(mouse_cursor, None);
+                                            }
+                                        } else {
                                             if let Some(mouse_cursor) = style.mouse_cursor {
                                                 window.set_cursor_style(mouse_cursor, Some(hitbox));
                                             }
@@ -1838,6 +1842,7 @@ impl Interactivity {
                 }
             });
         }
+        let drag_cursor_style = self.base_style.as_ref().mouse_cursor;
 
         let mut drag_listener = mem::take(&mut self.drag_listener);
         let drop_listeners = mem::take(&mut self.drop_listeners);
@@ -1929,6 +1934,7 @@ impl Interactivity {
                                         view: drag,
                                         value: drag_value,
                                         cursor_offset,
+                                        cursor_style: drag_cursor_style,
                                     });
                                     pending_mouse_down.take();
                                     window.refresh();
@@ -2269,6 +2275,7 @@ impl Interactivity {
                     }
                 }
 
+                style.mouse_cursor = drag.cursor_style;
                 cx.active_drag = Some(drag);
             }
         }