Make SqlNullabilityProcessor into a real ExpressionVisitor (#34697)

Closes #34696

Author: roji

src/EFCore.Relational/Query/SqlExpressions/SelectExpression.cs

@@ -4224,6 +4224,16 @@ public SelectExpression Update(
             return this;
         }
 
+        if (predicate is SqlConstantExpression { Value: true })
+        {
+            predicate = null;
+        }
+
+        if (having is SqlConstantExpression { Value: true })
+        {
+            having = null;
+        }
+
         var projectionMapping = new Dictionary<ProjectionMember, Expression>();
         foreach (var (projectionMember, expression) in _projectionMapping)
         {