Add support for opening links in incognito mode on Linux & BSD (#4745)

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/util/XDGHelper.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+#include "util/XDGDesktopFile.hpp"
+
+#include <QString>
+
+namespace chatterino {
+
+#if defined(Q_OS_UNIX) and !defined(Q_OS_DARWIN)
+
+std::optional<XDGDesktopFile> getDefaultBrowserDesktopFile();
+
+/// Parses the given `execKey` and returns the resulting program name, ignoring all arguments
+///
+/// Parsing is done in accordance to https://specifications.freedesktop.org/desktop-entry-spec/latest/ar01s07.html
+///
+/// Note: We do *NOT* support field codes
+QString parseDesktopExecProgram(const QString &execKey);
+
+#endif
+
+}  // namespace chatterino