debugger should warn if "program" property doesn't exist

[mousetraps]

Smoke testing, Windows

This would help diagnose potential typos/issues in launch.json (esp helpful if files have moved around)

[ramya-rao-a]

cc @roblourens thoughts?

Right now, we have a default which points to cwd if the program attribute is not specified

[roblourens]

Node debugger checks whether "program" exists, and fails if not.

[roblourens]

I don't know what delve is doing though

[ramya-rao-a]

@mousetraps When I delete the program property from launch.json and try debugging I get the below error "Failed to continue: "TypeError: Path must be a string. Received undefined"" which I believe is coming from VS Code itself.

Is that what you were referring to?