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.

Start by locating the debugger activation and configuration entry points in this repository, then compare them with the referenced activateMockDebug.ts example for resolveDebugConfiguration. Review the referenced package.json example for the Editor title area menu. Done means supporting debugging without launch.json and exposing the requested Play action in the editor title area.

Written by the indexing model from the issue text.