Support no launch.json debugging

Hi VS Code PM here 👋

We would love if firefox debug would support debugging without a `launch.json`. Thus allowing users to debug in a no folder vscode.
Easiest to do this is to have a dynamic `resolveDebugConfiguartion` that will provide a launch configuration on the fly. [Example](https://github.com/microsoft/vscode-mock-debug/blob/main/src/activateMockDebug.ts#L161)

Apart from that consider contributing to the Editor title area menu, such that a Play button would appear in the Editor Title area (picture below). Example how to do this https://github.com/microsoft/vscode-mock-debug/blob/main/package.json#L80

I think both of these are super important and would really love that we improve this experience 💯
Let me know if I can help somehow. I am also open to a quick 30 min meeting where we can discuss about the new cool VS Code debug features that firefox debug could potentially adopt.

まず、このリポジトリでデバッガーの有効化と構成のエントリポイントを見つけ、resolveDebugConfiguration 用の参照先の activateMockDebug.ts の例と比較します。Editor のタイトル領域メニューについて、参照先の package.json の例を確認します。launch.json なしでのデバッグをサポートし、エディターのタイトル領域に要求された Play アクションを表示できれば完了です。

索引モデルが issue の本文から書いたものです。