Attach debugger from integrated browser's toolbar

It would be handy to have an "Attach Debugger" action directly in the integrated browser's toolbar.
This would simply emulate the "Attach" Run Configuration, but would obviously skip tab selection. Plus, it'd mean I don't have to add yet another Run Configuration to `launch.json`.

```json
{
"name": "Attach to Integrated Browser",
"request": "attach",
"type": "editor-browser"
}
```