fix(validation): trim deep model error output

[jefflembeck]

• Replace JSON.parse/stringify with proper deepClone to avoid exponential escaping
• Add summarizeValidationErrors to limit error message size
• Add maxValidationErrorSize configuration option
• Fix issue Problem with validation when dealing with unions and deep models #1569 where validation errors could grow to 28KB-300MB

closes #1569

BREAKING CHANGE: Validation error messages for unions/intersections are now summarized when they exceed size limits

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