Add CWD parameter to child process spawn

[RedMickey]

Hello,
I am a maintainer of React Native Tools VS Code extension. The extension is used for debugging React Native (including Expo) applications.
We faced the issue, when we were trying to use dynamic project configuration and babel-plugin-dotenv-import. Our extension uses @expo/xdl package to start Expo server. But when the evalConfig method is being executed, we get an error that @env module doesn't exist. We found out that this happens due to incorrect CWD parameter in case of usage of this function within VS Code context. When we start the extension process.cwd isn't the same as the project root (on macOS it is /). But we found out that if we add correct CWD to spawn options, everything works fine.
This fix should increase the stability of evalConfig method work.

[superandrew]

watching this issue and supporting the PR!

[brentvatne]

this seems reasonable to me, thanks!

@RedMickey - would you be able to add a test case that covers the usage scenario you explained in your post, in order to ensure we don't regress on it?

cc @EvanBacon, will wait for you to approve

[RedMickey]

Hi @brentvatne, I've added tests to check process.cwd in a spawned child process.