Refactoring index constraints

[david-waltermire]

Committer Notes

• Refactored index constraints to use the new IIndex class. This will help in the future with further enhancements around use of indexes.
• Added and integrated a ConstraintValidationFinding builder for generating new findings.
• Improved error handling to emit validation errors instead of exceptions. This will result in the reporting of index lookup misses as findings.

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