Samples for status escalations

[davidjgoss]

🤔 What's changed?

• Mark undefined and ambiguous steps following a failed-ish step in the reference implementation, and add a new sample to cover this. Some implementations may not adopt this behaviour.
• Add a scenario to the "skipped" sample to cover existing behaviour around failed After hooks following a skipped step.

⚡️ What's your motivation?

Fixes #237.

🏷️ What kind of change is this?

• ⚡ New feature (non-breaking change which adds new behaviour)
• 💥 Breaking change (incompatible changes to the API)

📋 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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