cql3: expr: Add as_column_maybe_subscripted
cql3: expr: Add as_column_maybe_subscripted

Add a convenience function that allows to convert
a reference to expression to column_maybe_subscripted.

It will be useful in a moment.

For now part of it must be commented out
because subscript is not in the expression variant yet.

It will be uncommented once subscript is finally added
to expression.

Signed-off-by: Jan Ciolek <b66a6f3989e26cb552db14b7ab163c3a50292e24@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla