[Lambda] Layer: Show code source in Lambda Code Source Explorer

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**Tell us about your request**
Enable the Lambda code source explorer to display the code source of layer(s) associated with the function. The code could be read-only but would allow developers to view function definitions and documentation directly within the Lambda console.

**Which service(s) is this request for?**
AWS Lambda

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
Currently, when using Lambda layers, there is no direct way to view the source code of functions provided by the layer within the Lambda console. Developers must download .zip file of the layer's source code and read it externaly, which disrupts the workflow and makes debugging or hot fix harder.

**Additional context**
This feature would improve developer productivity by providing better visibility into layer contents.

**Attachments**
N/A

この依頼は、AWS Lambda Code Source Explorer と関数に関連付けられた layers に関するものです。リポジトリのファイル、テスト、実装のエントリーポイントは指定されていません。まず explorer と layer-source の処理箇所を見つけ、次に Lambda コンソールで layers が提供するコードとドキュメントを読み取り専用で直接表示して、完成した動作を確認してください。

索引モデルが issue の本文から書いたものです。