✨ add real bounding box

[ianardee]

✨ add real bounding box

API's polygon property is now set to the new field property polygon.

Existing field property bbox is now an actual calculated bounding box.

For OTS products this will have no effect, since currently polygons are always rectangular bounding boxes.

Will be useful when we transition custom docs to object fields.

Motivation and Context

Required work for Cropper feature and having classes in the custom document response.

How Has This Been Tested

New unit tests.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[fharper]

LGTM