Incorrect shaping around U+0AFB GUJARATI SIGN SHADDA

[dscorbett]

U+0AFB GUJARATI SIGN SHADDA is a gemination mark. It can occur in the middle of a cluster: the second example in section 4.2 of L2/15-103R is ⟨શૻ્શૻ⟩ (U+0AB6 U+0AFB U+0ACD U+0AB6 U+0AFB). If the shadda precedes the virama, as in that proposal, HarfBuzz inserts a dotted circle, because the shadda has Indic_Syllabic_Category=Cantillation_Mark. If the shadda follows the virama, as its Indic_Syllabic_Category implies is currently the correct order, the input is split into two clusters, whereas it should be one cluster with a half form.

See also roozbehp/unicode-data#7.