Show default mouse cursor over documentation panel (#3951)

[Task link](https://www.pivotaltracker.com/story/show/183970777)

The default mouse cursor is now displayed over the documentation panel.


https://user-images.githubusercontent.com/6566674/205954491-177fcc01-7e15-4a5c-825e-c0b02be527cc.mp4

app/gui/view/src/documentation.rs

@@ -279,12 +279,14 @@ impl View {
         let visualization_frp = visualization::instance::Frp::new(&frp.network);
         let model = Model::new(scene);
         model.load_waiting_screen();
-        Self { model, visualization_frp, frp }.init(scene)
+        Self { model, visualization_frp, frp }.init(app)
     }
 
-    fn init(self, scene: &Scene) -> Self {
+    fn init(self, app: &Application) -> Self {
         let network = &self.frp.network;
         let model = &self.model;
+        let scene = &app.display.default_scene;
+        let overlay = &model.overlay;
         let visualization = &self.visualization_frp;
         let frp = &self.frp;
         frp::extend! { network
@@ -320,6 +322,12 @@ impl View {
                 (new != old).as_some(new)
             });
             frp.source.is_selected <+ is_selected_changed;
+
+
+            // === Mouse Cursor ===
+
+            app.frp.show_system_cursor <+ overlay.events.mouse_over;
+            app.frp.hide_system_cursor <+ overlay.events.mouse_out;
         }
         visualization.pass_events_to_dom_if_active(scene, network);
         self

lib/rust/ensogl/core/src/application.rs

@@ -41,6 +41,10 @@ pub mod traits {
 crate::define_endpoints_2! {
     Input {
         set_tooltip(tooltip::Style),
+        /// Show the system mouse cursor.
+        show_system_cursor(),
+        /// Hide the system mouse cursor.
+        hide_system_cursor(),
     }
     Output {
         tooltip(tooltip::Style)
@@ -75,6 +79,15 @@ pub struct ApplicationData {
     update_themes_handle: callback::Handle,
 }
 
+impl ApplicationData {
+    /// Show or hide the system mouse cursor by setting the `cursor` CSS property of the `body`
+    /// element.
+    fn show_system_cursor(&self, show: bool) {
+        let style = if show { "auto" } else { "none" };
+        web::document.body_or_panic().set_style_or_warn("cursor", style);
+    }
+}
+
 impl Application {
     /// Constructor.
     pub fn new(dom: impl DomPath) -> Self {
@@ -89,13 +102,8 @@ impl Application {
         let themes = theme::Manager::from(&display.default_scene.style_sheet);
         let cursor = Cursor::new(&display.default_scene);
         display.add_child(&cursor);
-        web::document.body_or_panic().set_style_or_warn("cursor", "none");
         let update_themes_handle = display.on.before_frame.add(f_!(themes.update()));
         let frp = Frp::new();
-        let _network = frp.network();
-        enso_frp::extend! { _network
-            frp.private.output.tooltip <+ frp.private.input.set_tooltip;
-        }
 
         let data = ApplicationData {
             logger,
@@ -109,7 +117,22 @@ impl Application {
             frp,
         };
 
-        Self { inner: Rc::new(data) }
+        Self { inner: Rc::new(data) }.init()
+    }
+
+    fn init(self) -> Self {
+        let frp = &self.frp;
+        let data = &self.inner;
+        let network = self.frp.network();
+        enso_frp::extend! { network
+            frp.private.output.tooltip <+ frp.private.input.set_tooltip;
+            eval_ frp.private.input.show_system_cursor(data.show_system_cursor(true));
+            eval_ frp.private.input.hide_system_cursor(data.show_system_cursor(false));
+        }
+        // We hide the system cursor to replace it with the EnsoGL-provided one.
+        self.frp.hide_system_cursor();
+
+        self
     }
 
     /// Create a new instance of a view.