Add support for iTwin Geospatial Features API

[jjspace]

Description

• Adds initial support for the OGC WFS Geospatial Features API through ITwinData.loadGeospatialFeatures
• Updates the iTwin Feature Service Sandcastle to use the new API

Issue number and link

No issue, follow up for #12344

Testing plan

• Load the iTwin Feature Service sandcastle and make sure it still works

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @jjspace!

✅ We can confirm we have a CLA on file for you.