[Visual C++] Allow child process debugging

WinDbg has the .childdbg option which will automatically cause the debugger to attach to child processes when the parent calls CreateProcess.

GDB has a similar option, where you can set it to follow forks. #511 is related, and a workaround is offered in the comments to enable setting the follow fork mode to on. But this is not the ideal solution, because it doesn't provide any solution for the Windows Debug Engine, cppvsdbg. It would be nice if the launch.json configuration supported a simple boolean variable, debugChildProcess which you could set to true or false. By default it's false, and the user can override it.

Inizia tracciando come vengono analizzate le opzioni di launch.json e passate a Windows Debug Engine (cppvsdbg), usando come contesto il workaround per follow-fork in #511. Il lavoro è completo quando è supportata un’opzione booleana debugChildProcess, con valore predefinito false, che abilita il debugging dei processi figli per i motori di debugging interessati senza modificare il comportamento predefinito.