Returns root-level tuple validation errors combined with
per-position validation results.
The returned value has both NestedValidationResult properties
(errors, isValid, descriptor, seenValue) and indexed
position results ([0], [1], etc.).
Validation result type returned by
TupleSchemaBuilder.validate(). ExtendsValidationResultwithgetNestedErrorsfor root-level tuple errors and per-position validation results.