Add support for the debug server to windows

[directionless]

Problem

Launcher has always shipped a debug server. This is enabled by sending SIGUSR1 to the launcher process. Unfortunately, windows does not support signals, so this has never been enabled on windows.

Solution

Use a filesystem based switch instead. To be honest, I don't love polling the filesystem, but from what I can tell, it's that or create a socket for RPC communication.

I probably need to test this a little bit more.