The write path uses a base schema at a particular version, and we
want it to use the materialized views at the corresponding version.
To achieve this, we need to map the state currently in db::view::view
to a particular schema version, which this patch does by introducing
the view_info class to hold the state previously in db::view::view,
and by having a view schema directly point to it.
The changes in the patch are thus:
1) Introduce view_info to hold the extra view state;
2) Point to the view_info from the schema;
3) Make the functions in the now stateless db::view::view non-member;
4) Remove the db::view::view class.
All changes are structural and don't affect current behavior.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>