Move desktop notifications to its own header

We'll need to use this from the chainloader.

src/common/notifications.h

@@ -0,0 +1,58 @@
+// yabridge: a Wine plugin bridge
+// Copyright (C) 2020-2022 Robbert van der Helm
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+#pragma once
+
+// This header is used by the plugins and the chainloaders to send desktop
+// notifications when something goes wrong
+
+#include <ghc/filesystem.hpp>
+#include <optional>
+
+// TODO: At some point, provide an alternative to notify-send by dlopen()-ing
+//       libdbus instead. Some more obscure distros won't have notify-send
+//       available.
+
+/**
+ * Send a desktop notification using `notify-send`. Used for diagnostics when a
+ * plugin fails to load since the user may not be checking the output in a
+ * terminal.
+ *
+ * @param title The title (or technically, summary) of the notification.
+ * @param body The message to display. This can contain line feeds, and it any
+ *   HTML tags and XML escape sequences will be automatically escaped. The
+ *   message can also be empty.
+ * @param origin If this is set to the current plugin's path, then the
+ *   notification will append a 'Source: <XXX.so>' hyperlink to the body so the
+ *   user can more easily navigate to the plugin's path.
+ *
+ * @return Whether the notification was sent. This will be false if
+ *   `notify-send` is not available.
+ */
+bool send_notification(const std::string& title,
+                       const std::string body,
+                       std::optional<ghc::filesystem::path> origin);
+
+/**
+ * Escape XML entities within a string. Used inside of desktop notifications.
+ */
+std::string xml_escape(std::string string);
+
+/**
+ * URL encode a file path. We won't escape forward slashes, and `path` should
+ * not yet include the `file://` prefix.
+ */
+std::string url_encode_path(std::string path);