We were missing support in the "CAST(x AS type)" function for the counter
type. This patch adds this support, as well as extensive testing that it
works in Scylla the same as Cassandra.
We also un-xfail an existing test translated from Cassandra's unit
test. But note that this old test did not cover all the edge-cases that
the new test checks - some missing cases in the implementation were
not caught by the old test.
Fixes#14501
Signed-off-by: Nadav Har'El <nyh@scylladb.com>