Slow stepping when debugging Typescript repos

[isidorn]

Investigate again why the stepping is slow when debuggin the Typescript repository (steps take 1 second). More details can be found here #5645
fyi @egamma

[weinand]

Please try for both protocols.

[isidorn]

I have compared the performance while debugging the checker.ts file in the typescript repository. Below I have attached three gifs illustrating this. The first one is the inspector protocol debugger which shows very good stepping performance (indistinguishable from debugging a simple file). The second shows the legacy adapter which is in the current insiders / stable and the third shows the legacy adapter with a logging bugfix made by @weinand. When comparing these two it seems like the bugfix did not have a noticable impact on the performance.

Current slowness shown only by the node adapter is due the old node debug protocol returning more data than asked for. @weinand would have to dig more in order to find the exect culprit, however that might not be necessery since we are moving towards using the inspector protocol in any case.

User workaround to get a good experience: add "protocol": "inspector" to your launch.json or update to node version 8 or greater (since then we will automatically pick the new inspector protocol)

Also created a related issue for case with much more local variables #25296

fyi @egamma