cql3: expr: Handle subscript in fill_prepare_context
cql3: expr: Handle subscript in fill_prepare_context

fill_prepare_context collects useful information about
the expression involved in query restrictions.

We should collect this information from subscript as well,
just like we do from column_value and its sub.

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

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