startDebugging option to merge debug console with parent

[isidorn]

Refs #62419

As stated there
Using many debug consoles for multi-process debugging is painful in many situations.

We need a config flag to turn this off such that all debug output goes in one debug console. Since this situation arrises with sessions that are automatically created via API we would like to add an option to the startDebugging API to control this.

PR which tackles this #80673

[isidorn]

Added it to vscode.proposed.d.ts
Created #81170 as a reminder to move it from proposed to offical api next milestone