Add more Property / Loader integration test combinations

This is an extension of #676. The initial implementation created a framework for bulk testing and added tests for several loaders and Properties, but not all of them. Finish that off by including every loader and every existing Property.

The current work is in a separate module, [here](https://github.com/eeverman/andhow/tree/main/andhow-testing/andhow-core-integration-test).