If the fon supports Graphite features we can get the feature
descriptions from the font, but this descriptions are mostly
limited (available in a limited number of languages), so it is
better to only use this descriptions only if the feature does not
have an OpenType description available.

Change-Id: Ic0b81cb8cc22e1e73f30e6a960167cfa982fbfc7
Reviewed-on: https://gerrit.libreoffice.org/56318
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>