fix(windows): configure hidden and grabbed cursor

This fixes issues where a hidden and grabbed cursor could leave the
window and become visible on top of the windows taskbar (and potentially
leave the window altogether if the taskbar is clicked) under at least
two occasions:

    - When a window is overlapping the taskbar.
    - When a window is maximized and Automatically hide the taskbar has
      been enabled.

This approach of confining the cursor to the center of the window is
used in SDL.

src/changelog/unreleased.md

@@ -40,3 +40,4 @@
 - **Breaking:** Removed `EventLoopBuilder::with_user_event`, the functionality is now available in `EventLoop::with_user_event`.
 - Add `Window::default_attributes` to get default `WindowAttributes`.
 - `log` has been replaced with `tracing`. The old behavior can be emulated by setting the `log` feature on the `tracing` crate.
+- On Windows, confine cursor to center of window when grabbed and hidden.

src/platform_impl/windows/window_state.rs

@@ -510,7 +510,22 @@ impl CursorFlags {
 
         if util::is_focused(window) {
             let cursor_clip = match self.contains(CursorFlags::GRABBED) {
-                true => Some(client_rect),
+                true => {
+                    if self.contains(CursorFlags::HIDDEN) {
+                        // Confine the cursor to the center of the window if the cursor is hidden. This avoids
+                        // problems with the cursor activating the taskbar if the window borders or overlaps that.
+                        let cx = (client_rect.left + client_rect.right) / 2;
+                        let cy = (client_rect.top + client_rect.bottom) / 2;
+                        Some(RECT {
+                            left: cx,
+                            right: cx + 1,
+                            top: cy,
+                            bottom: cy + 1,
+                        })
+                    } else {
+                        Some(client_rect)
+                    }
+                }
                 false => None,
             };