Add Automated Testing

[kgar]

Add automated testing for Tidy 5e Sheets.

• Automated Testing: Build First Test #3
• Be able to test all essential sheet capabilities in all supported versions of Foundry.
• Be able to test sheet compatibility with hand-picked modules, such as Popout.
• Verify that the API has not been broken.
• Stretch: Be able to run this test in a Github action.
• Stretch: Provide a documentation paper trail / report that is automatically generated based on the tests and their assertions, to explain the expectations of functionality, available as an artifact on the Github action (and potentially elsewhere?)

Ongoing effort

This is a project unto itself. As test cases are determined, we'll create Automated Testing issues as enhancements. When all known test cases relating to Tidy 5e Sheets as a standalone module are satisfied for the present time, the project will conclude, and further test cases will just be standalone issues.