new
Creates a new #GDesktopAppInfo based on a desktop file id.
A desktop file id is the basename of the desktop file, including the .desktop extension. GIO is looking for a desktop file with this name in the applications subdirectories of the XDG data directories (i.e. the directories specified in the XDG_DATA_HOME and XDG_DATA_DIRS environment variables). GIO also supports the prefix-to-subdirectory mapping that is described in the Menu Spec (i.e. a desktop id of kde-foo.desktop will match /usr/share/applications/kde/foo.desktop).
Return
a new #GDesktopAppInfo, or null if no desktop file with that id exists.
Parameters
desktopId
the desktop file id