New API in glibmm 2.64

Member Glib::build_filename (const String1& elem1, const String2& elem2, const Strings&...strings)
Member Glib::canonicalize_filename (StdStringView filename, StdStringView relative_to=nullptr)
Member Glib::get_host_name ()
Member Glib::get_user_runtime_dir ()
Member Glib::MainContext::get_thread_default ()
Member Glib::MainContext::pop_thread_default ()
Member Glib::MainContext::push_thread_default ()
Class Glib::StdStringView
Class Glib::UStringView