When searching for font features, use Graphtie if it is available
instead of HarfBuzz, because HarfBuzz will only give a subset of
OpenType features in a Graphite font, but will ignore additional
features specific to Graphite.

Change-Id: I00c8790ee4d1e1ab906928f649d2a3e54163557f
Reviewed-on: https://gerrit.libreoffice.org/58306
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>