Function SzConfigTool_addExpressionFunction 

#[unsafe(no_mangle)]
pub extern "C" fn SzConfigTool_addExpressionFunction(
    config_json: *const c_char,
    efunc_code: *const c_char,
    connect_str: *const c_char,
    efunc_desc: *const c_char,
    language: *const c_char,
) -> SzConfigTool_result

Add an expression function