Refactor to use node-ipc protocol in tests

[remcohaszing]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)
• If applicable, I’ve added docs and tests

Description of changes

This allows us to use the console, which is useful for debugging.

This also simplifies how paths are resolved in tests. I combined these changes, because they touch the same lines.

[wooorm]

• Looks like this fails on windows
• Can you clarify how the console can be used?
• Otherwise fine

[remcohaszing]

Can you clarify how the console can be used?

stdout and stderr are now inherited from the parent process. It’s not used by the language client anymore. This means you can just write anything using console.log(), console.dir(), or whatever you like in the test and it will show up in the terminal.