Function resolve_sql_function_drop_target 

pub fn resolve_sql_function_drop_target(
    catalog: &dyn RoutineNameCatalog,
    registry: &BTreeMap<String, Vec<Arc<SQLUserFunction>>>,
    item: &DropFunctionItem,
    requested_types: Option<&[String]>,
    is_procedure: bool,
    expected_kind: &str,
) -> Result<Option<(String, usize)>, SQLError>

Find the routine a DROP item names; requested_types are its argument types resolved to catalog type names.