Mutatingcopyable keypath

[bdunay3]

Description

This PR adds an additional method to MutatingCopyable that uses KeyPath instead of a closure to mutate a property on a struct and return a new copy of that struct with the modifications. Unit tests included.

Type of Change

• [ ] Bug Fix
• [x] New Feature
• [ ] Breaking Change
• [ ] Refactor
• [ ] Documentation
• [ ] Other (please describe)

Checklist

• [x] I have read the contributing guidelines
• [x] Existing issues have been referenced (where applicable)
• [x] I have verified this change is not present in other open pull requests
• [x] Functionality is documented
• [x] All code style checks pass
• [x] New code contribution is covered by automated tests
• [x] All new and existing tests pass