WIP: add E2E test suite unrelated to docs examples

This is ongoing, bear with me while I hack on this :<
The main reason is the `baseUrl` line --- as far as I can tell, the docs tests always try to load fixtures relative to the served docs folder, and the non-docs tests are basically always relative to the project durectory. I'm ot sure if it's possible to have a `baseUrl` dependent on which specs are used