chore: deprecate things from the entry point

[davidjgoss]

🤔 What's changed?

• Several things newly deprecated, where use cases are better served by the new JavaScript API
  • Cli
  • PickleFilter
  • Runtime
• Standardised the way we deprecate things - many of them are still used internally (for now) and we just want to stop exposing them to consumers, so we handle the deprecations on the entry point
• Documented the deprecations and what our process is

⚡️ What's your motivation?

We need to pare down what's exported so we can funnel people to use the new API and we can be free to refactor internals which currently difficult with things like Cli and Runtime being effectively part of the interface contract.

🏷️ 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 (+0.002%) to 98.255% when pulling 954340d on deprecations-before-9 into 7f43644 on main.