Function map_column_refs 

fn map_column_refs<'a>(
    cols: &'a [UnresolvedItemName],
    option_type: SqlServerConfigOptionName,
) -> Result<BTreeMap<SqlServerQualifiedTableName, BTreeSet<&'a str>>, PlanError>

Create a BTreeMap of SqlServerQualifiedTableName to a BTreeSet of column names.