Add helper method for platform independent file path building

[Chris0296]

Throughout the project "/" is used as a delimiter for file paths. This is specific to Linux/Mac OS. This PR adds a helper method which uses Apache Commons IO FilenameUtils.concat function to build platform independent file paths

Github Issue: https://github.com/cqframework/cqf-tooling/issues/187

• [x] I've read the contribution guidelines
• [x] Code compiles without errors
• [x] Tests are created / updated
• [ ] Documentation is created / updated

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