[HarfBuzz] Telugu support

[Shriramana Sharma]

Hi -- Telugu also has archaic repha feature and fonts can provide a
repha glyph. See details at
https://sites.google.com/site/jamadagni/files/utcsubmissions/12017-telugu-reph-model-finalize.pdf

The sequence to select repha is RA + VIRAMA + ZWJ since by default
Telugu normally does not use repha. I have uploaded repha glyph for
Lohit Telugu just now:
https://bugzilla.redhat.com/show_bug.cgi?id=841947

It would be great if you could add repha support for Telugu while you
are at it! Thanks!

-- 
Shriramana Sharma