[Tech Debt] Convert to use Test Plans

[joshuatbrown]

Xcode Test Plans are the modern way to configure tests. They allow for multiple targets as well as multiple configurations; we could use them to test multiple localizations, for example. They also provide a bit more visibility into what's enabled and what's disabled. This last benefit would help us as we currently have three tests disabled but it's not very clear that they are.

https://useyourloaf.com/blog/xcode-test-plans/