Make YamlValidator filepaths platform agnostic

[abaskk-msft]

Problem

• The repo is meant to be platform agnostic, the YamlValidator isn't. This PR attempts to make code involving filepaths and their test platform agnostic.

Notes

• Tests became more verbose since the filepath type and directory path is determined at runtime and had to be moved out of DataRows.

Validation

• re-ran unit tests
• Tested Locally