Function interp_hashmap_keys 

fn interp_hashmap_keys(
    args: &[RValue],
    named: &[(String, RValue)],
    context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Return all keys of a HashMap as a character vector.

The order of keys is not guaranteed (HashMap is unordered).

@param h integer scalar: hashmap ID @return character vector of keys