Major Description
When saving the model containing some computed columns using functions of `timestampdiff` or `timestampadd`, it failed with throwing an exception as follows.
This happens because `ModelSemanticHelper#discardInvalidComputedColumnsForBrokenModel` used the `innerExpression` of the computed column other than `expression`. By design, the `innerExpression` is used for spark, the expression used by calcite parser.
