Add new methods for attachments, hooks, meta

[davidjgoss]

🤔 What's changed?

Adds three new methods in our polyglot, test case-centric interface:

• findAttachmentsBy(TestStepFinished) returns an array of attachments. TestStepFinished makes the most sense as the starting point because it has both the testStepId to identify the step, and the testCaseStartedId to identify the test case attempt.
• findHookBy(TestStep) returns an optional Hook, natural cousin of findPickleStepBy(TestStep)
• findMeta() returns the Meta message if present

Also, fixes a bug in the old attachment-related method in JavaScript, which made an assumption an attachment would always be tied to a testStepId, which will not be the case once cucumber/messages#102 is implemented in runners.

⚡️ What's your motivation?

Required for work on React components for the HTML formatter in cucumber/html-formatter#283

🏷️ What kind of change is this?

• 🏦 Refactoring/debt/DX (improvement to code design, tooling, etc. without changing behaviour)
• ⚡ New feature (non-breaking change which adds new 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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[mpkorstanje]

Looks good. Few nitpicks. Feel free to merge after addressing these.