Fixes#19070
The `neq` operator in `compute-where-condition-parts.ts` uses `OR` where
it should use `AND` when handling null-equivalent values.
Currently generates:
```sql
field != '' OR field IS NOT NULL
```
For a row where `field = ''`:
- `'' != ''` = false
- `'' IS NOT NULL` = true
- `false OR true` = true -- row incorrectly passes the filter
The `eq` operator correctly uses `OR field IS NULL` because it's
additive (match value or its null equivalent). By De Morgan's law, the
negation `neq` needs `AND field IS NOT NULL` -- exclude if the value
doesn't match AND is not a null equivalent.
With the fix:
```sql
field != '' AND field IS NOT NULL
```
- `'' != ''` = false, `'' IS NOT NULL` = true, `false AND true` = false
-- correctly excluded
- `NULL != ''` = NULL, `NULL IS NOT NULL` = false, `NULL AND false` =
false -- correctly excluded
- `'Alice' != ''` = true, `'Alice' IS NOT NULL` = true, `true AND true`
= true -- correctly included
Affects `neq` filters on TEXT fields and all composite sub-fields
(firstName, lastName, primaryEmail, primaryPhoneNumber, address
sub-fields, etc.) when filtering against null-equivalent values.
Co-authored-by: Etienne <45695613+etiennejouan@users.noreply.github.com>
