Make buttons unpress when the cursor leaves the button rect.

Implement this functionality by adding global cursor tracking.
It's currently only possible for one GWidget per GWindow to track the cursor.

Kernel/ProcessGUI.cpp

@@ -244,3 +244,16 @@ int Process::gui$set_window_rect(int window_id, const GUI_Rect* rect)
     WSMessageLoop::the().server_process().request_wakeup();
     return 0;
 }
+
+int Process::gui$set_global_cursor_tracking_enabled(int window_id, bool enabled)
+{
+    if (window_id < 0)
+        return -EINVAL;
+    auto it = m_windows.find(window_id);
+    if (it == m_windows.end())
+        return -EBADWINDOW;
+    auto& window = *(*it).value;
+    WSWindowLocker locker(window);
+    window.set_global_cursor_tracking_enabled(enabled);
+    return 0;
+}