Improve Math block behavior when importing and replacing schemas

### Description
When a policy's math block has variables, and I update an Excel based schema and then import it and replace existing schemas, I want the math block configuration and to be preserved and any errors resulting from the import to be flagged for review and corrective action.

### Context
Math block input variables and formulas are schema dependent. Improve the math block so that reimporting a schema does not wipe the math block configuration. If the schema path references found within a math block become invalid due to schema updates (e.g. a key is renamed or removed), the user is notified of the validation error so that the reference can be reviewed and corrected.

### Acceptance Criteria
* replacing a schema does not alter the math block configration (such as variables, formulas, tabs etc)
* validate schema references within the math block after a schema re-import operation
* invalid schema references are flagged as errors with suggested corrective actions per existing interaction patterns