Fixed #36198 -- Implemented unresolved transform expression replacement.

This allows the proper resolving of F("field__transform") when
performing constraint validation.

Thanks Tom Hall for the report and Sarah for the test.

tests/constraints/models.py

@@ -73,6 +73,7 @@ class UniqueConstraintProduct(models.Model):
     name = models.CharField(max_length=255)
     color = models.CharField(max_length=32, null=True)
     age = models.IntegerField(null=True)
+    updated = models.DateTimeField(null=True)
 
     class Meta:
         constraints = [