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/examples/drag_drop.rs

@@ -0,0 +1,137 @@
+use gpui::{
+    App, Application, Bounds, Context, Half, Hsla, Pixels, Point, Window, WindowBounds,
+    WindowOptions, div, prelude::*, px, rgb, size,
+};
+
+#[derive(Clone, Copy)]
+struct DragInfo {
+    ix: usize,
+    color: Hsla,
+    position: Point<Pixels>,
+}
+
+impl DragInfo {
+    fn new(ix: usize, color: Hsla) -> Self {
+        Self {
+            ix,
+            color,
+            position: Point::default(),
+        }
+    }
+
+    fn position(mut self, pos: Point<Pixels>) -> Self {
+        self.position = pos;
+        self
+    }
+}
+
+impl Render for DragInfo {
+    fn render(&mut self, _: &mut Window, _: &mut Context<'_, Self>) -> impl IntoElement {
+        let size = gpui::size(px(120.), px(50.));
+
+        div()
+            .pl(self.position.x - size.width.half())
+            .pt(self.position.y - size.height.half())
+            .child(
+                div()
+                    .flex()
+                    .justify_center()
+                    .items_center()
+                    .w(size.width)
+                    .h(size.height)
+                    .bg(self.color.opacity(0.5))
+                    .text_color(gpui::white())
+                    .text_xs()
+                    .shadow_md()
+                    .child(format!("Item {}", self.ix)),
+            )
+    }
+}
+
+struct DragDrop {
+    drop_on: Option<DragInfo>,
+}
+
+impl DragDrop {
+    fn new() -> Self {
+        Self { drop_on: None }
+    }
+}
+
+impl Render for DragDrop {
+    fn render(&mut self, _window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        let items = [gpui::blue(), gpui::red(), gpui::green()];
+
+        div()
+            .size_full()
+            .flex()
+            .flex_col()
+            .gap_5()
+            .bg(gpui::white())
+            .justify_center()
+            .items_center()
+            .text_color(rgb(0x333333))
+            .child(div().text_xl().text_center().child("Drop & Drop"))
+            .child(
+                div()
+                    .w_full()
+                    .mb_10()
+                    .justify_center()
+                    .flex()
+                    .flex_row()
+                    .gap_4()
+                    .items_center()
+                    .children(items.into_iter().enumerate().map(|(ix, color)| {
+                        let drag_info = DragInfo::new(ix, color);
+
+                        div()
+                            .id(("item", ix))
+                            .size_32()
+                            .flex()
+                            .justify_center()
+                            .items_center()
+                            .border_2()
+                            .border_color(color)
+                            .text_color(color)
+                            .cursor_move()
+                            .hover(|this| this.bg(color.opacity(0.2)))
+                            .child(format!("Item ({})", ix))
+                            .on_drag(drag_info, |info: &DragInfo, position, _, cx| {
+                                cx.new(|_| info.position(position))
+                            })
+                    })),
+            )
+            .child(
+                div()
+                    .id("drop-target")
+                    .w_128()
+                    .h_32()
+                    .flex()
+                    .justify_center()
+                    .items_center()
+                    .border_3()
+                    .border_color(self.drop_on.map(|info| info.color).unwrap_or(gpui::black()))
+                    .when_some(self.drop_on, |this, info| this.bg(info.color.opacity(0.5)))
+                    .on_drop(cx.listener(|this, info: &DragInfo, _, _| {
+                        this.drop_on = Some(*info);
+                    }))
+                    .child("Drop items here"),
+            )
+    }
+}
+
+fn main() {
+    Application::new().run(|cx: &mut App| {
+        let bounds = Bounds::centered(None, size(px(800.), px(600.0)), cx);
+        cx.open_window(
+            WindowOptions {
+                window_bounds: Some(WindowBounds::Windowed(bounds)),
+                ..Default::default()
+            },
+            |_, cx| cx.new(|_| DragDrop::new()),
+        )
+        .unwrap();
+
+        cx.activate(true);
+    });
+}