[arabic-table] Further tune

In anticipation of Unicode 7.0 data coming in the next commit.
[arabic-table] Add ZWJ/ZWNJ now that table is segmented
[arabic-table] Update to Unicode 7.0

Old table was from 6.2.  Remove hard-coded Mongolian and Phags-pa data.
This completes support for new scripts Manichian and Psaltar Pahlavi.
Minor: format
[indic-table] Update to Unicode 6.3.0

Was from 6.2.0.  It's a no-op.  Committing for the record.
[indic-table-gen] Minor
Minor
Add new IndicSyllabicCategory short forms for Unicode 7.0
Add back API removed recently

Add hb_ot_layout_language_get_required_feature_index() again, which
is used in Pango.  This was removed in
da132937989acb4d8ca9bd41c79f98750e7dda30 in favor of
hb_ot_layout_language_get_required_feature().

API changes:

  - Added hb_ot_layout_language_get_required_feature_index back.