Handle Cucumber Expression optionals not preceded by space in suggestions

[aslakhellesoy]

🤔 What's changed?

Optional text is now included in the suggestion unless it's preceded by a word (in which case it becomes suggestion options).

⚡️ What's your motivation?

The reason we include the optional in the text is that we cannot present a ['the ', ''] option to the user (where one of the options is an empty string). It cannot be represented in an LSP snippet choice

Also, this fixes #45

🏷️ 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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