`IS [NOT] NULL` does not work with complex types

[hatyo]

Let's assume we have the following schema:

create type as struct nested(a bigint, b bigint)
create table t2(id bigint, col1 nested, primary key(id))
insert into t2 values (1, null), (2, (5, 6))

The following query throws a semantic analysis exception:

select * from t2 where col1 is null

also this one throws a similar exception:

select * from t2 where col1 is not null

The exception is:

com.apple.foundationdb.record.query.plan.cascades.SemanticException: The comparand to a comparison expecting an argument of a primitive type, is invoked with an argument of a complex type, e.g. an array or a record.

this is due to having a very strict verification against passing a record type to single-parameter RelOp values which I think should be allowed. Moreover, the IS_NULL and IS_NOT_NULL encapsulators lack support for RECORD type arguments, this should be fixed.