Promote standalone component helpers to public API

### Command

add

### Description

With https://github.com/angular/angular-cli/commit/e895fc7c1012796442cb7a4a3b9b3a0ec3845b0e a few standalone helpers were moved from the CDK to the schematics package. I am wondering why they were moved to a "private" section and aren't considered public API. Was this just because standalone components were still in developer preview at that time? Now that angular 15 is going to make standalone components stable could the helpers be moved outside the private section and be treated as public API?

### Describe the solution you'd like

With standalone components becoming stable these helpers should become public API as well.

### Describe alternatives you've considered

_No response_

從提交 e895fc7c1012796442cb7a4a3b9b3a0ec3845b0e 開始，檢查從 CDK 移至 schematics 套件的獨立 helper。確定 private 區段如何公開它們，然後驗證這些 helper 是否被視為 public API；如果該套件有相關 coverage，則更新或新增它。

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