WIP: Check for case sensitivity rather than branching on OS type

[JamesWTruher]

PR Summary

A couple of tests use the OS type to make a determination as to whether there's a case sensitive file system. In some environment (say a Linux container, or a specific configuration of Linux), this is not sufficient. I've added some direct checks for determining case sensitivity on the file system, and then use that in the tests.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.