Implement `is [not] distinct from` predicate

We aim to add support for these expressions to enable null-safe (in)equality comparisons as specified in the SQL:2023 standard:

```
<distinct predicate> ::=
    <row value predicand 3> <distinct predicate part 2>

<distinct predicate part 2> ::=
    IS [ NOT ] DISTINCT FROM <row value predicand 4>
```