support: record step keyword, deprecate defineStep

[davidjgoss]

🤔 What's changed?

Rework our functions for defining steps - without changing the API or behaviour yet - so that we record the step keyword for Given, When and Then.

defineStep which allowed you to define a step without a keyword is now deprecated, and we'll remove it probably in 9.0.0 in a few months. In the meantime it records the step as a Given, which means we could progress with this feature before removing defineStep from the API if we want.

⚡️ What's your motivation?

First step in solving #2043 - we're recording the step keyword now, so later we'll be able to start using that to check against the pickle keyword when we introduce the stricter behaviour.

🏷️ What kind of change is this?

• 🏦 Refactoring/debt/DX (improvement to code design, tooling, documentation etc. without changing behaviour)

📋 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 increased (+0.004%) to 98.297% when pulling 66621f6 on feat/record-step-keyword into 1e0831c on main.