Support tuple IN VALUES for SQLite, others

Support tuple IN VALUES for SQLite, others

Added support for composite (tuple) IN operators with SQLite, by rendering
the VALUES keyword for this backend.  As other backends such as DB2 are
known to use the same syntax, the syntax is enabled in the base compiler
using a dialect-level flag ``tuple_in_values``.   The change also includes
support for "empty IN tuple" expressions for SQLite when using "in_()"
between a tuple value and an empty set.

Fixes: #4766
Change-Id: I416e1af29b31d78f9ae06ec3c3a48ef6d6e813f5