Predicate functions for General_Category

[echeran]

For use cases in which we want to request the General_Category property value for a given code point (ex: iterating through text per-code point), we should provide predicate functions that allow the user to query whether the returned property value is included in the multi-category values.

The General_Category property value describes the 30 "simple" property values (Uppercase_Letter, Lowercase_Letter, ...), which are the what is returned for the first API described above.

The multi-category values (also described as "derived" values) are logically set unions of other General_Category values (Cased_Letter, Letter, Mark, ...). Just like in ICU, we need predicate functions that correspond to each multi-category value (is_cased_letter(...) -> bool, is_letter(...) -> bool, ...) that return a boolean when the input belongs to the corresponding logical set.