Function is_cursive_script_cluster 

pub fn is_cursive_script_cluster(c: &ShapedCluster) -> bool

Returns true if the cluster’s first character belongs to a cursive script (Arabic, Syriac, Mongolian, N’Ko, Mandaic, Phags Pa, Hanifi Rohingya) per CSS Text 3 Appendix D. These scripts should not have letter-spacing applied.