[ios, build] Add tests for MGLMapView pitch setting and tilt gesture

[friedbunny]

Part of #14091 — adds tests for MGLMapView pitch setting and for the tilt gesture recognizer.

• Still a slight work in progress, as setting pitch to a negative value seems like it shouldn’t do anything, but currently results in a value of 60. Update: pitch is indeed not settable to negative values — it leaves the camera’s original value intact.
• I may also add a test for [ios] Require two fingers for duration of tilt gesture #14969.

/cc @julianrex @fabian-guerra

[friedbunny]

@julianrex this is ready for review — I added more tests and split out others into their own test methods.

[julianrex]

Looks good - just a couple of comments/questions.

[julianrex]

👍