Before this rev:

* Take 2 domains that contain at least two leaves, and at least one of
them must use the implicit `&` operator

e.g.:
```python
    d1 = [('so_line', 'in', [91]), ('amount', '<=', 0.0)]
    d2 = ['&', ('so_line', 'in', []), ('project_id', '!=', False)]
```

* Perform osv.expression.OR() between both domains

Expected result:
```python
    d3 = ['|', d1, d2]
```

Actual result (after normalization):
```
    d3 = ['&', '|', d1, d2]
```

This is because, since the `&` is implicit for the first domain, when we
OR it, we give it an explicit `|` operator, so when we pass this domain
through the normalize_domain function, d1 no longer contains an implicit
`&` operator but instead the implicit operator is the one between d1 and
d2, therefore giving us a completely wrong domain.

The `combine` function states that it only accepts normalized domains,
however neither the OR nor AND functions do, this leads to a lot of
developers putting non-normalized domains into these functions, and
there's no error checking or anything that obviously indicates that the
domain is incorrect, so we might as well normalize all domains being
passed since it's already pretty optimized.

Task-ID: 1833909