cql3: Implement maps::literal::test_assignment() function
cql3: Implement maps::literal::test_assignment() function

The test_assignement() function is invoked via the Cassandra unit tests
so we might as well implement it.

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@scylladb.com>

raphaelsc/scylla,duarten/scylla,avikivity/scylla,kjniemi/scylla,raphaelsc/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,kjniemi/scylla,kjniemi/scylla,duarten/scylla,raphaelsc/scylla