Fix Reqnroll.VisualStudio 173 Regex modifiers treated as step parameters

[clrudolphi]

🤔 What's changed?

The RegexStepDefinitionAnalyzer was refactored to support the inclusion of regex modifiers.

The main logic flow was significantly restructured in an attempt to make it more human readable (eliminating nested IFs in favor of case statements).

⚡️ What's your motivation?

Fix #173.

🏷️ What kind of change is this?

• 🐛 Bug fix (non-breaking change which fixes a defect)

♻️ Anything particular you want feedback on?

📋 Checklist:

• 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 "[vNext]" section of the CHANGELOG, linking to this pull request & included my GitHub handle to the release contributors list.

---

This text was originally taken from the template of the Cucumber project, then edited by hand. You can modify the template here.