db/virtual_table: Add a way to specify a range of partitions for virtual table queries.
db/virtual_table: Add a way to specify a range of partitions for virtual
table queries.

This change introduces a query_restrictions object into the virtual
table infrastructure, for now only holding a restriction on partition
ranges.
That partition range is then implemented into
memtable_filling_virtual_table.

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