Support splitting out composite action steps [GA]

### Value Prop

Customers appreciate the way composite actions enable them to easily take multiple steps and repeat them easily in jobs. However, they also wish to split out the steps within the job rather than keeping it within the composite action. This increases readability and makes it easy for users to analyze individual steps.

### Expected Outcome
Enable composite actions to split out their steps within a job, rather than being treated as a single composite entity.

该 issue 描述了一个 GitHub Actions 路线图请求，但没有指出实现文件、测试或入口点。首先确定 composite action 的执行和 job 步骤展示分别在哪里实现；当 composite-action 步骤在 job 中逐个显示且保持其行为时，即视为完成。

由索引模型根据 Issue 内容生成。