Send "relpath" back for all test files/folders.

[ericsnowcurrently]

(for #6758)

The key changes:

• leave node IDs alone (do not normcase)
• preserve the "relpath" of each file/folder
• send that relpath back in the results
• generate "TestFile.fullPath" (in discovery parser) using relpath instead of ID

There is also a bunch of cleanup (in cases where the code was cluttered enough that I was worried about missing something). (sorry) If that is a problem then let me know and we can walk through the PR.

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• [ ] Has a news entry file (remember to thank yourself!)
• Appropriate comments and documentation strings in the code
• [ ] Has sufficient logging.
• [ ] Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• [ ] Test plan is updated as appropriate
• [ ] package-lock.json has been regenerated by running npm install (if dependencies have changed)
• [ ] The wiki is updated with any design decisions/details.

[ericsnowcurrently]

FYI, I know what the problem is in Windows CI and will fix it soon.

[karrtikr]

As far as the key changes go, this looks good to me.