default stderr if not provided to Cli ctor

[davidjgoss]

🤔 What's changed?

In Cli, default the stderr property of the constructor object to process.stderr if it's not defined - making the property effectively optional for consumers.

⚡️ What's your motivation?

We introduced this property in #2137 which was effectively a breaking change for people who use the Cli class for framework integrations. It managed to fly under the radar until https://github.com/cucumber/cucumber-js/pull/2092/files#diff-7f71b0d311e14868f853f726912b222ac5e2aee58d985f1758d6b8f5e19c4c5c (8.5.2) where there'll be an error if it's missing. This affects nightwatch for example (see #2137).

This class will shortly be deprecated in favour of runCucumber et al, but in the meantime it should be stable.

🏷️ What kind of change is this?

• 🐛 Bug fix (non-breaking change which fixes a defect)

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

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[coveralls]

Coverage remained the same at 98.236% when pulling bf8d9c8 on fix/cli-stderr into 01368ca on main.