convert `Measure` class to enum

[jordanbrauer]

Types of changes

What types of changes does your code introduce? Check/place an x in all the boxes that apply:

• [ ] 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)
• [x] I have read the CONTRIBUTING document.
• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

Description

WIP

Motivation and Context

upgrading to modern php and adopting it's features

How Has This Been Tested?

unit tests

Screenshots:

N/A