Add tests for every example

[friedbunny]

We currently only have tests that use XCUITest to run through every example, but this 1. does nothing to check correctness, and 2. is quite slow.

We should have goals to:

1. Check that every example does what we intend.
2. Make the tests runnable individually.
3. Add tests with every new example as a requirement before merging.
4. Prioritize reliability — failures must be meaningful and addressed immediately.

Thoughts

• We should investigate other UI testing libraries, like KIF and earlgrey.
• If tests are made faster and more reliable, we can run them on more simulators.

/cc @mapbox/maps-ios