如果提示被屏蔽，将填充 blockReason 和相关的 safetyRatings。
签名：
export interface PromptFeedback
属性
| 属性 | 类型 | 说明 |
|---|---|---|
| blockReason | BlockReason | |
| blockReasonMessage | 字符串 | |
| safetyRatings | 安全等级[] |
PromptFeedback.blockReason
签名：
blockReason: BlockReason;
PromptFeedback.blockReasonMessage
签名：
blockReasonMessage?: string;
PromptFeedback.safetyRatings
签名：
safetyRatings: SafetyRating[];