Right now, binary_operator::lhs is a variant<column_value,
std::vector<column_value>, token>. The role of the second branch
(a vector of column values) is to represent a tuple of columns
e.g. "WHERE (a, b, c) = ?"), but this is not clear from the type
name.
Inroduce a wrapper type around the vector, column_value_tuple, to
make it clear we're dealing with tuples of CQL references (a
column_value is really a column_ref, since it doesn't actually
contain any value).
Closes#8208
bd16e98019