Support Grapheme Boundary Rule GB9c

[tarekgh]

Unicode 16.0 introduced a new Grapheme boundary rule GB9c. Most likely this will need to read a new Unicode file IndicSyllabicCategory.txt to extract the Consonant and Virama character list to be able to implement this rule according to the InCB definition.

When implementing this rule, we need to enable the test for rule [9.3] when reading the test data

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[tarekgh]

CC @GrabYourPitchforks