Migrate config towards selecting server script path, rather than root directory

[mxsdev]

The vscode-js-debug recently switched folder structure from building to out to building to dist.

This breaks the codebase since I (in retrospect, rather stupidly) hard-coded the out/src/vsDebugServer.js path. Probably, the configuration for debugger_path should be to the script rather than the parent folder.

I don't wanna break existing installations, so probably it's best to add a config like debugger_script_path and try to phase out the old debugger_path.