This change extends kashida justification to Syriac, using custom
insertion rules.
Change-Id: I7508d2c32e95abb12a098e989c7153828ba81c87
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/173990
Tested-by: Jenkins
Reviewed-by: Jonathan Clark <jonathan@libreoffice.org>