Agentic autofix generation for code scanning alerts [Public Preview]

### Value Prop

You can now assign code scanning alerts directly to copilot for automatic fixes, saving time and effort on security issues. This makes it easier to keep your code secure and up to date without manual intervention.

### Expected Outcome

We want to help you resolve code scanning alerts faster and with less work, so you can focus on building features instead of fixing vulnerabilities. By automating the fix process, we aim to improve your workflow efficiency and overall code security.

该 issue 描述了将 code scanning 警报分配给 Copilot 以进行自动修复，但没有指定实现文件、测试或入口点。首先明确 public preview 的预期范围和验收标准；完成的标准应包括一条已达成共识的实现路径，以及一种验证警报是否获得适当自动修复的方法。

由索引模型根据 Issue 内容生成。