Some legacy evaluators do not support target output key

[akshaylive]

... such as LLM as a judge evaluator. Please fix.

Please refer to LegacyExactMatchEvaluator for a potential fix.

My suggestion is to create a def get_targeted_field(self, obj: Any) -> Any: in LegacyBaseEvaluator. Then, modify all evaluators to perform

actual_output = self.get_targeted_field(agent_execution.agent_output)
expected_output = self.get_targeted_field(evaluation_criteria.expected_output)

[akshaylive]

BTW the impl in LegacyExactMatchEvaluator may not be fully correct. Specifically, if target key is not present, the right thing to do may be to provide an error. Please verify.