Materialized Views: fill virtual columns
Materialized Views: fill virtual columns

The add_cells_to_view() function usually adds selected cells from the base
table to the view mutation. For issue #3362, we sometimes want to also
add unselected cells as "virtual" cells -  truncated versions of the
base-table cells just without the values.

This patch contains the code to fill the virtual columns' data using the
regular columns from the base table.

This patch does not yet actually *add* any virtual columns to the schema,
so until that is done (in the next patch), this patch will not yet cause
any behavior change. This is important for bisectability.

Refs #3362.

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>

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