Starting to debug should be snappier

This is based on my VS Code selfhosting of the debug feature. Startup to debug always feels janky and laggy because the following things happen in between noticeable millisecond intervals: 1. I press <kbd>F5</kbd> 2. The debug toolbar appears 3. The Debug viewlet is focused 4. The debug toolbar shows a dropdown since it knows there are multiple debug targets 5. The status bar turns orange I think all 5 things should occur _immediately_ even if the result of the operation won't work due to some error. I think something specific to our selfhost is our dependance on the `Ensure Prelaunch Dependencies` pre-launch task, which takes ~1 second on my machine. This makes up for very noticeable lag which I attribute to the tool being slow.