实现思路:如果一个面的所有边都是凹边,那么这个面就是槽或者刻字的底面,然后通过该面找其相邻面就可以获取槽或者刻字的所有面
PK_linkage_m PK_ERROR_code_t PK_EDGE_ask_convexity
(/* received */PK_EDGE_t /*edge*/,const PK_EDGE_ask_convexity_o_t * /*options*/,/* returned */PK_EDGE_convexity_t * /*convexity*/
);