## Summary of the Pull Request
New year, new unittests.
This PR introduces a new project, `TestHostApp`. This project is largely taken from the TAEF samples, and allows us to easily construct a helper executable and `resources.pri` for running TerminalApp unittests.
## References
## PR Checklist
* [x] Closes#3986
* [x] I work here
* [x] is Tests
* [n/a] Requires documentation to be updated
* [x] **Waiting for an updated version of TAEF to be available**
## Detailed Description of the Pull Request / Additional comments
Unittesting for the TerminalApp project has been a horrifying process to try getting everything pieced together just right. Dependencies need to get added to manifests, binplaced correctly, and XAML resources need to get compiled together as well. In addition, using a MUX `Application` (as opposed to the Windows.UI.Xaml `Application`) has led to additional problems.
This was always a horrifying house of cards for us. Turns out, the reason this was so horrible is that the test infrastructure for doing what we're doing _literally didn't exist_ when I started doing all that work last year.
So, with help from the TAEF team, I was able to get rid of our entire house of cards, and use a much simpler project to build and run the tests.
Unfortunately, the latest TAEF release has a minor bug in it's build rules, and only publishes the x86 version of a dll we need from them. But, the rest of this PR works for x86, and I'll bump this when that updated version is available. We should be able to review this even in the state it's in.
## Validation Steps Performed
ran the tests yo
3fcc935782